Ton (US) to Atomic Mass Unit Converter
Convert US tons to atomic mass units with our free online weight converter.
Quick Answer
1 Ton (US) = 5.463194e+29 atomic mass units
Formula: Ton (US) × conversion factor = Atomic Mass Unit
Use the calculator below for instant, accurate conversions.
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Ton (US) to Atomic Mass Unit Calculator
How to Use the Ton (US) to Atomic Mass Unit Calculator:
- Enter the value you want to convert in the 'From' field (Ton (US)).
- The converted value in Atomic Mass Unit will appear automatically in the 'To' field.
- Use the dropdown menus to select different units within the Weight category.
- Click the swap button (⇌) to reverse the conversion direction.
How to Convert Ton (US) to Atomic Mass Unit: Step-by-Step Guide
Converting Ton (US) to Atomic Mass Unit involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Ton (US) = 5.46319e+29 atomic mass unitsExample Calculation:
Convert 5 US tons: 5 × 5.46319e+29 = 2.73159e+30 atomic mass units
Disclaimer: For Reference Only
These conversion results are provided for informational purposes only. While we strive for accuracy, we make no guarantees regarding the precision of these results, especially for conversions involving extremely large or small numbers which may be subject to the inherent limitations of standard computer floating-point arithmetic.
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View all Weight conversions →What is a Ton (US) and a Atomic Mass Unit?
What Is a US Ton?
The US ton (officially called the short ton) is a unit of mass in the United States customary measurement system, defined as:
- Exactly 2,000 pounds (avoirdupois pounds)
- Exactly 32,000 ounces
- Exactly 907.18474 kilograms (by definition from 1959 international agreement)
- 20 hundredweight (where 1 hundredweight = 100 pounds in US system)
The US ton is the standard unit for measuring heavy loads in American commerce, transportation regulations, construction materials, and industrial applications.
US Ton vs. Metric: Key Comparison
US Ton (Short Ton):
- 2,000 pounds (exactly)
- 907.185 kilograms (907.18474 kg precisely)
- Used in United States for trucks, cargo, materials
- Based on 2,000-pound commercial standard
Metric Tonne:
- 1,000 kilograms (exactly)
- 2,204.623 pounds (about 2,205 lb)
- Global standard for international trade, shipping, emissions
- Based on metric system (1,000 kg)
Visual comparison:
- A metric tonne is about 92.8 kg heavier than a US ton (about 205 lb more)
- 1 metric tonne = 1.102 US tons (about 10% heavier)
- 1 US ton = 0.907 metric tonnes (about 10% lighter)
Commercial impact: A 20-ton truck in the US (40,000 lb) equals 18.14 metric tonnes. A 20-tonne truck in Europe (20,000 kg) equals 22.05 US tons. This distinction matters for international shipping, vehicle regulations, and trade contracts.
US Ton vs. Long Ton (UK)
US Ton (Short Ton):
- 2,000 pounds (20 hundredweight × 100 lb)
- 907.185 kg
- Standard in United States
Long Ton (Imperial Ton, UK):
- 2,240 pounds (20 hundredweight × 112 lb)
- 1,016.047 kg
- 12% heavier than US ton
- Used historically in UK, now largely replaced by metric tonne
Difference: The long ton is 240 pounds heavier than the US ton. This originated from different definitions of "hundredweight"—the US uses 100 lb, while the UK traditionally used 112 lb.
When it matters: Historical shipping documents, UK coal trade, and older engineering specifications may reference "tons" meaning long tons (2,240 lb), not US short tons (2,000 lb).
What Is an Atomic Mass Unit?
The atomic mass unit (symbol: u), also called the unified atomic mass unit or Dalton (symbol: Da), is a unit of mass used for expressing atomic and molecular masses.
Official definition: 1 u = exactly 1/12 of the mass of one unbound carbon-12 atom at rest in its ground state
Value in SI units: 1 u = 1.660 539 066 60 × 10⁻²⁷ kg (with uncertainty ±0.000 000 000 50 × 10⁻²⁷ kg)
Why Use Atomic Mass Units Instead of Kilograms?
Atomic and molecular masses in kilograms are extraordinarily small and unwieldy:
In kilograms (impractical):
- Hydrogen atom: 1.674 × 10⁻²⁷ kg
- Water molecule: 2.992 × 10⁻²⁶ kg
- Glucose molecule: 2.990 × 10⁻²⁵ kg
In atomic mass units (convenient):
- Hydrogen atom: 1.008 u
- Water molecule: 18.015 u
- Glucose molecule: 180.16 u
The atomic mass unit scales numbers to manageable sizes while maintaining precision for chemical calculations.
Carbon-12: The Reference Standard
Why carbon-12?
- Exact definition: ¹²C is defined as exactly 12 u (no uncertainty)
- Abundant: Carbon-12 comprises 98.89% of natural carbon
- Stable: Not radioactive, doesn't decay
- Central element: Carbon forms countless compounds, making it ideal for chemistry
- Integer mass: Convenient reference point (mass = 12 exactly)
Historical context: Before 1961, physicists and chemists used different oxygen-based standards, creating two incompatible atomic mass scales. Carbon-12 unified them.
Dalton vs. Unified Atomic Mass Unit
Two names, same unit:
Unified atomic mass unit (u):
- Official SI-accepted name
- Used primarily in chemistry and physics
- Symbol: u
Dalton (Da):
- Alternative name honoring John Dalton
- Used primarily in biochemistry and molecular biology
- Symbol: Da
- Convenient for large molecules (kilodaltons, kDa)
Relationship: 1 u = 1 Da (exactly equivalent)
Usage patterns:
- "The oxygen atom has a mass of 16.0 u" (chemistry)
- "The antibody protein has a mass of 150 kDa" (biochemistry)
Both refer to the same fundamental unit.
Note: The Ton (US) is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Atomic Mass Unit belongs to the imperial/US customary system.
History of the Ton (US) and Atomic Mass Unit
Etymology: The "Tun" Wine Cask
The word "ton" derives from the medieval "tun," a large wine barrel or cask used for transporting and storing wine. A standard tun held approximately 252 wine gallons and weighed roughly 2,000 pounds when full.
This practical origin meant "ton" became synonymous with "very heavy load"—approximately the weight that could be carried in one tun cask. The measurement evolved from this real-world shipping container into a standardized unit of weight.
English Origins: Competing Ton Standards
In medieval and early modern England, multiple "ton" standards coexisted, creating confusion in commerce:
1. Wine Ton (Tun): ~2,000 pounds, based on wine cask weight 2. Long Ton: 2,240 pounds, based on 20 long hundredweight (20 × 112 lb) 3. Shipping Ton: Volume-based, used for calculating cargo space, not weight
The long ton (2,240 lb) became the official British standard, formalized in the British Imperial system in 1824. It was calculated as 20 hundredweight, where 1 hundredweight (cwt) = 112 pounds (8 stone × 14 lb/stone).
The short ton (2,000 lb) remained in common commercial use, especially in trades dealing with bulk commodities. It represented 20 hundredweight of 100 pounds each, a simpler rounding for everyday commerce.
American Adoption: The Short Ton (2,000 Pounds)
When American colonists inherited English measurement systems, both long ton (2,240 lb) and short ton (2,000 lb) were in use. After independence, the United States faced a choice between standardizing on one or the other.
Reasons the US chose the short ton (2,000 lb):
- Simpler arithmetic: 2,000 is easier to divide and calculate than 2,240
- Commercial preference: The 2,000-pound ton was already common in American trade
- Hundredweight definition: The US standardized on 100-pound hundredweight (rather than 112 lb), making 20 × 100 = 2,000 lb logical
- Decimal thinking: 2,000 fits better with base-10 calculations
In 1832, the US Treasury Department formally adopted the 2,000-pound ton as the standard US ton, distinguishing it as the "short ton" to differentiate from the British "long ton" (2,240 lb).
Metric Definition (1959)
The 1959 International Yard and Pound Agreement refined the US ton's definition in metric terms:
- 1 pound = 0.45359237 kilograms (exactly)
- 1 US ton = 2,000 pounds = 907.18474 kilograms (exactly)
This metric definition ended ambiguity about the ton's exact mass in international contexts and established clear conversion factors for trade between US customary and metric systems.
Modern Usage: Persistent in US, Metric Elsewhere
Today, the US ton remains dominant in American industry despite global metrication:
Why the US ton persists in America:
- Transportation regulations: Federal trucking regulations use tons (Gross Vehicle Weight Rating in tons)
- Construction pricing: Gravel, sand, concrete priced per ton (2,000 lb)
- Cultural inertia: Generations of American industry built around ton-based systems
- Equipment design: Trucks, scales, loading equipment calibrated in tons
Global trend toward metric tonnes:
- International shipping: Maritime cargo measured in metric tonnes (1,000 kg)
- Carbon emissions: Greenhouse gases measured in tonnes CO2 (metric)
- Scientific use: Research and engineering use metric tonnes exclusively
- Trade contracts: International agreements specify metric tonnes to avoid confusion
Result: The US is the only major economy still using short tons as the primary heavy-weight standard, requiring constant conversion for international commerce.
John Dalton and Atomic Theory (1803-1808)
John Dalton (1766-1844), an English chemist and physicist, revolutionized chemistry with his atomic theory (1803):
Dalton's key postulates:
- All matter consists of indivisible atoms
- Atoms of the same element are identical in mass and properties
- Atoms of different elements have different masses
- Chemical compounds form when atoms combine in simple whole-number ratios
Relative atomic masses: Dalton created the first table of atomic weights (1805-1808), assigning hydrogen a mass of 1 and expressing other elements relative to it:
- Hydrogen: 1
- Oxygen: 7 (incorrect; should be ~16, but Dalton thought water was HO, not H₂O)
- Carbon: 5 (incorrect)
Though Dalton's numerical values were often wrong (he didn't yet know correct chemical formulas), his conceptual framework established that elements have characteristic atomic masses.
Berzelius and Improved Atomic Weights (1810s-1820s)
Jöns Jacob Berzelius (Swedish chemist, 1779-1848) refined Dalton's work with meticulous experiments:
Achievements:
- Determined accurate atomic weights for over 40 elements by 1818
- Established oxygen = 100 as the standard (for convenience in calculation)
- Introduced modern chemical notation (H, O, C, etc.)
Berzelius' atomic weights were remarkably accurate, many within 1% of modern values.
Cannizzaro and Avogadro's Number (1860)
Stanislao Cannizzaro (Italian chemist, 1826-1910) resolved confusion about atomic vs. molecular weights at the Karlsruhe Congress (1860):
Key insight: Avogadro's hypothesis (1811)—equal volumes of gases contain equal numbers of molecules—allows distinguishing atomic from molecular masses
Result: By 1860s, chemists adopted consistent atomic weights based on oxygen = 16
The Oxygen Standard Era (1890s-1960)
Chemist's standard (1890s onward):
- Natural oxygen (mixture of ¹⁶O, ¹⁷O, ¹⁸O) = 16.0000 exactly
- Practical for analytical chemistry
- Used in atomic weight tables
Physicist's standard (1900s onward):
- Oxygen-16 isotope (¹⁶O) = 16.0000 exactly
- Used in mass spectrometry and nuclear physics
- More precise for isotope work
The problem: Natural oxygen is 99.757% ¹⁶O, 0.038% ¹⁷O, and 0.205% ¹⁸O
- Chemist's scale and physicist's scale differed by ~0.0003 (0.03%)
- Small but significant for precision work
Unification: Carbon-12 Standard (1961)
1960 IUPAP resolution (International Union of Pure and Applied Physics):
- Proposed carbon-12 as the new standard
- Physicist Alfred Nier championed the change
1961 IUPAC resolution (International Union of Pure and Applied Chemistry):
- Adopted carbon-12 standard
- Defined: 1 atomic mass unit = 1/12 the mass of ¹²C atom
Advantages of carbon-12:
- Unified physics and chemistry scales
- Carbon is central to organic chemistry
- Mass spectrometry reference (carbon calibration)
- Abundant, stable, non-radioactive
Notation evolution:
- Old: amu (atomic mass unit, ambiguous—which standard?)
- New: u (unified atomic mass unit, unambiguous—carbon-12 standard)
The Dalton Name (1960s-1980s)
1960s proposal: Several scientists suggested naming the unit after John Dalton
1980s acceptance: The name "Dalton" (Da) gained widespread use in biochemistry
1993 IUPAC endorsement: Officially recognized "Dalton" as an alternative name for the unified atomic mass unit
Modern usage:
- Chemistry/physics: Prefer "u" (atomic mass unit)
- Biochemistry: Prefer "Da" (Dalton), especially with kDa (kilodaltons) for proteins
Mass Spectrometry and Precision (1900s-Present)
Mass spectrometry (developed 1910s-1920s, refined continuously):
Thomson and Aston (1910s-1920s):
- J.J. Thomson and Francis Aston developed early mass spectrographs
- Discovered isotopes by precise mass measurement
- Aston won 1922 Nobel Prize in Chemistry
Modern precision:
- Mass spectrometry now measures atomic masses to 8-10 decimal places
- Essential for determining isotopic compositions
- Used to measure the carbon-12 standard with extraordinary accuracy
CODATA values: The Committee on Data for Science and Technology (CODATA) publishes official atomic mass unit values every few years, incorporating latest measurements:
- 2018 value: 1 u = 1.660 539 066 60(50) × 10⁻²⁷ kg
2019 SI Redefinition
Historic change: On May 20, 2019, the International System of Units (SI) was redefined based on fundamental physical constants rather than physical artifacts (like the kilogram prototype)
New kilogram definition: Based on the Planck constant (h = 6.626 070 15 × 10⁻³⁴ J·s, exact)
Impact on atomic mass unit: The atomic mass unit is now indirectly tied to fundamental constants through the kilogram's new definition, though it remains defined as 1/12 the mass of carbon-12
Practical effect: Minimal—atomic masses remain effectively unchanged, but now rooted in unchanging physical constants
Common Uses and Applications: US tons vs atomic mass units
Explore the typical applications for both Ton (US) (imperial/US) and Atomic Mass Unit (imperial/US) to understand their common contexts.
Common Uses for US tons
1. Trucking and Transportation Regulations
Federal trucking regulations:
- Weight limits: Federal limit 80,000 lb (40 tons) gross vehicle weight on interstate highways
- Bridge formulas: Determine allowable weight based on axle spacing
- Weight stations: Weigh trucks to ensure compliance (fines for overweight)
Vehicle classification by GVWR:
- Class 1-2: Up to 10,000 lb (5 tons) — pickups, vans
- Class 3: 10,001-14,000 lb (5-7 tons) — heavy-duty pickups
- Class 4-6: 14,001-26,000 lb (7-13 tons) — box trucks, delivery trucks
- Class 7-8: 26,001-80,000 lb (13-40 tons) — semis, dump trucks, tractor-trailers
Commercial driver's license (CDL) requirements:
- CDL required: Vehicles over 26,000 lb (13 tons) GVWR
- Special endorsements: Hazmat, tanker, double/triple trailers
2. Construction and Building Materials
Material purchasing:
- Bulk materials: Gravel, sand, topsoil, mulch ordered by the ton
- Delivery trucks: 10-ton, 15-ton, 20-ton capacity standard sizes
- Pricing: Per-ton pricing typical ($20-$100/ton depending on material)
Structural engineering:
- Load calculations: Building load capacity measured in tons (tons per square foot)
- Crane capacity: Cranes rated by maximum lift capacity in tons (e.g., 50-ton crane)
- Equipment weight: Bulldozers, excavators specified by operating weight in tons
Concrete and cement:
- Ready-mix trucks: 8-10 cubic yard capacity (~16-20 tons wet concrete)
- Cement bags: 94 lb bags; ~21 bags = 1 ton cement
- Foundation loads: Structural loads calculated in tons
3. Waste Management and Environmental Services
Municipal solid waste:
- Collection fees: Often based on tonnage (residential flat fee, commercial per ton)
- Landfill tipping fees: $30-$100 per ton (varies by region, landfill type)
- Transfer stations: Weigh incoming waste by ton for billing and tracking
Recycling markets:
- Material pricing: Cardboard, metals, plastics traded by ton
- Scrap metal: Auto scrap, structural steel sold by ton to recyclers
- Commodity markets: Recycled materials priced per ton (fluctuates with demand)
Environmental reporting:
- Emissions: Industrial facilities report emissions in tons (NOx, SOx, PM)
- Waste reduction goals: "Divert 10,000 tons from landfills annually"
- Composting: Organic waste diverted measured in tons
4. Maritime and Port Operations
Cargo handling (US ports):
- Container weights: Listed in both tons (US) and metric tonnes (international)
- Crane capacity: Gantry cranes rated in tons lifting capacity
- Ballast water: Ship ballast measured in tons
Vessel tonnage (historical short ton use):
- Gross tonnage (GT): Volume-based ship size measurement (100 cubic feet = 1 register ton)
- Deadweight tonnage (DWT): Weight capacity, now primarily metric tonnes
- Displacement tonnage: Weight of water displaced, traditionally long tons, now metric
US domestic shipping:
- Great Lakes shipping: Often uses short tons for iron ore, coal, grain shipments
- Coastal shipping: Barge loads measured in tons
5. Industrial Manufacturing
Raw material purchasing:
- Steel, aluminum, copper: Purchased by the ton
- Chemicals: Bulk chemicals ordered in ton quantities
- Plastics: Resin pellets sold by ton
Production capacity:
- Steel mill: "Produces 2 million tons steel per year"
- Cement plant: "10,000 tons clinker production per day"
- Paper mill: "500 tons paper production per day"
Heavy machinery:
- Equipment weight: Specified in tons (e.g., "150-ton hydraulic press")
- Material handling: Forklifts, cranes rated by ton capacity
- Foundry operations: Ladle capacity measured in tons of molten metal
6. Agriculture and Commodity Trading
Crop production:
- Yield reporting: "Harvested 5,000 tons corn" or "200 bushels/acre"
- Storage: Grain elevators capacity measured in tons
- Trading: Commodity futures traded in tons or metric tonnes
Livestock operations:
- Feed consumption: "Dairy consumes 1,500 tons feed per year"
- Manure management: Measured in tons for spreading, composting
- Livestock hauling: Trailer capacity rated in tons
Farm equipment:
- Tractor weight: Specified in tons (affects traction, field compaction)
- Implements: Plow, harrow weight measured in tons
7. Energy and Mining
Coal industry:
- Mining production: Measured in tons per day/year
- Transportation: Coal trains (100+ cars × 100 tons = 10,000+ ton trains)
- Power generation: Plant fuel consumption measured in tons/day
Mining operations:
- Ore extraction: Production measured in tons mined per day
- Haul trucks: Mining dump trucks carry 100-400 tons per load
- Processing capacity: "Processes 50,000 tons ore per day"
Oil and gas (weight measurements):
- Equipment: Drilling rigs, platforms specified by weight in tons
- Offshore installations: Platform deck capacity measured in tons
When to Use atomic mass units
1. Atomic Weights and Periodic Table
The periodic table lists atomic weights (average masses) of elements in atomic mass units:
Example: Carbon:
- Natural carbon contains 98.89% ¹²C (12.0000 u) and 1.11% ¹³C (13.0034 u)
- Weighted average: 0.9889 × 12.0000 + 0.0111 × 13.0034 = 12.0107 u
- Periodic table lists carbon's atomic weight as 12.011 u
Why atomic weights aren't integers: Most elements are mixtures of isotopes with different masses, so the average is non-integer
Usage: Every stoichiometry calculation in chemistry depends on atomic weights expressed in u or g/mol (numerically equal)
2. Molecular Mass Calculations
Molecular mass = sum of atomic masses of all atoms in the molecule
Example: Glucose (C₆H₁₂O₆):
- 6 carbon atoms: 6 × 12.011 = 72.066 u
- 12 hydrogen atoms: 12 × 1.008 = 12.096 u
- 6 oxygen atoms: 6 × 15.999 = 95.994 u
- Total: 72.066 + 12.096 + 95.994 = 180.156 u
Molar mass connection: 180.156 u per molecule = 180.156 g/mol (numerically identical!)
3. Mass Spectrometry
Mass spectrometry measures the mass-to-charge ratio (m/z) of ions:
Technique:
- Ionize molecules (add or remove electrons)
- Accelerate ions through electric/magnetic fields
- Separate by mass-to-charge ratio
- Detect and measure abundances
Output: Mass spectrum showing peaks at specific m/z values (in u/e or Da/e, where e = elementary charge)
Applications:
- Determining molecular formulas
- Identifying unknown compounds
- Measuring isotope ratios
- Protein identification in proteomics
- Drug testing and forensics
Example: A peak at m/z = 180 for glucose (C₆H₁₂O₆ = 180 u, charge = +1e)
4. Protein Characterization (Biochemistry)
Biochemists routinely express protein masses in kilodaltons (kDa):
SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis):
- Separates proteins by molecular weight
- Gels calibrated with protein standards of known kDa
- "The unknown protein band migrates at ~50 kDa"
Protein databases:
- UniProt, PDB (Protein Data Bank) list protein masses in Da or kDa
- Essential for identifying proteins by mass
Clinical diagnostics:
- "Elevated levels of 150 kDa IgG antibodies detected" (immune response)
- Tumor markers identified by protein mass
5. Stoichiometry and Chemical Equations
Stoichiometry: Calculating quantities in chemical reactions
Example: Combustion of methane: CH₄ + 2O₂ → CO₂ + 2H₂O
Molecular masses:
- CH₄: 16.043 u
- O₂: 31.998 u
- CO₂: 44.010 u
- H₂O: 18.015 u
Mass balance: 16.043 + 2(31.998) = 44.010 + 2(18.015) = 80.039 u (both sides equal, confirming conservation of mass)
Practical calculation: To produce 44 grams of CO₂, you need 16 grams of CH₄ and 64 grams of O₂
6. Isotope Analysis
Isotopes: Atoms of the same element with different numbers of neutrons (different masses)
Examples:
- ¹²C: 12.0000 u (6 protons, 6 neutrons) — 98.89% of natural carbon
- ¹³C: 13.0034 u (6 protons, 7 neutrons) — 1.11% of natural carbon
- ¹⁴C: 14.0032 u (6 protons, 8 neutrons) — radioactive, trace amounts
Applications:
- Radiocarbon dating: ¹⁴C decay measures age of organic materials
- Climate science: ¹³C/¹²C ratios in ice cores track ancient temperatures
- Medical tracers: ¹³C-labeled compounds track metabolic pathways
- Forensics: Isotope ratios identify geographic origins of materials
7. Nuclear Physics and Mass Defect
Mass-energy equivalence (E = mc²): Mass and energy are interconvertible
Mass defect: The mass of a nucleus is slightly less than the sum of its individual protons and neutrons
Example: Helium-4 (⁴He):
- 2 protons: 2 × 1.007276 = 2.014552 u
- 2 neutrons: 2 × 1.008665 = 2.017330 u
- Sum: 4.031882 u
- Actual ⁴He nucleus mass: 4.001506 u
- Mass defect: 4.031882 - 4.001506 = 0.030376 u
Interpretation: The "missing" 0.030376 u was converted to binding energy that holds the nucleus together
Calculation: 0.030376 u × c² = 28.3 MeV (million electron volts)
This is the energy released when helium-4 forms from protons and neutrons (nuclear fusion).
Additional Unit Information
About Ton (US) (ton)
How many pounds are in a US ton?
There are exactly 2,000 pounds (lb) in 1 US ton (short ton).
Quick conversion:
- 1 ton = 2,000 lb
- 0.5 ton = 1,000 lb
- 2 tons = 4,000 lb
- 10 tons = 20,000 lb
This is the defining relationship: the US ton is defined as exactly 2,000 avoirdupois pounds.
Is the US ton the same as the UK ton?
No. The US ton (short ton) is smaller than the traditional UK ton (long ton):
- US ton (short ton): 2,000 lb = 907.185 kg
- UK long ton: 2,240 lb = 1,016.047 kg
- Difference: The long ton is 240 lb (12%) heavier than the US ton
Modern UK usage: Today, the UK primarily uses metric tonnes (1,000 kg = 2,205 lb), not long tons. Long tons are historical and rarely used in modern commerce.
When it matters: Historical shipping documents, old engineering specifications, and traditional industries (coal mining, maritime) may reference long tons.
What is the difference between a ton and a tonne?
"Ton" (US short ton) and "tonne" (metric tonne) are different units:
US Ton (Short Ton):
- 2,000 pounds (exactly)
- 907.185 kilograms
- Used in United States
- Symbol: ton, st, US ton
Metric Tonne:
- 1,000 kilograms (exactly)
- 2,204.6 pounds
- Used internationally
- Symbol: t, tonne, MT
Key difference: The metric tonne is about 10% heavier (93 kg or 205 lb more) than the US ton.
Spelling note: "Tonne" (with "ne") specifically means metric tonne; "ton" can mean US short ton or UK long ton, requiring clarification.
How do you convert US tons to metric tonnes?
To convert US tons to metric tonnes, multiply by 0.907185 (or approximately 0.9):
Formula:
metric tonnes = US tons × 0.907185
Examples:
- 1 ton = 0.907 tonnes (just under 1 tonne)
- 10 tons = 9.07 tonnes (about 10% lighter)
- 100 tons = 90.7 tonnes
Reverse conversion (tonnes to tons):
US tons = metric tonnes × 1.102311
- 1 tonne ≈ 1.102 tons (about 10% heavier)
- 10 tonnes ≈ 11.02 tons
Practical approximation: For rough estimates, 1 ton ≈ 0.9 tonnes, or 1 tonne ≈ 1.1 tons.
Where is the US ton used?
The US ton (short ton) is primarily used in the United States for:
Industries and applications:
- Transportation: Trucking regulations, vehicle weight ratings (GVWR)
- Construction: Pricing gravel, sand, concrete, steel by the ton
- Waste management: Landfill fees, recycling tonnages
- Shipping: Domestic cargo weights, freight billing
- Agriculture: Crop yields, livestock feed, commodity trading
- Mining: Coal production, ore extraction
- Manufacturing: Steel, cement, paper production
International use: Almost all other countries use metric tonnes (1,000 kg) instead of US tons. The US is the only major economy still using short tons as the primary heavy-weight standard.
Trade caution: International shipping and trade contracts typically specify metric tonnes to avoid confusion between US tons, long tons, and metric tonnes.
What does "half-ton truck" mean?
"Half-ton truck" is a historical classification for light-duty pickup trucks, not a precise measurement of payload capacity.
Traditional meaning: Originally, "half-ton" meant the truck could carry approximately 1,000 lb (0.5 ton) payload.
Modern reality: Today's "half-ton" trucks (Class 2A) typically have payload capacities of 1,500-2,500 lb (0.75-1.25 tons)—often exceeding the historical "half-ton" rating.
Common "half-ton" models:
- Ford F-150
- Chevrolet Silverado 1500
- Ram 1500
- Toyota Tundra
- Nissan Titan
Other truck classifications:
- Half-ton (Class 2A): ~6,000-7,000 lb GVWR, ~1,500-2,000 lb payload
- Three-quarter-ton (Class 2B): ~8,500-10,000 lb GVWR, ~2,500-3,500 lb payload
- One-ton (Class 3): ~10,000-14,000 lb GVWR, ~3,000-4,500 lb payload
Important: Always check the vehicle's GVWR (Gross Vehicle Weight Rating) and payload capacity listed on the door jamb sticker or owner's manual, not the truck's name.
How much does a ton of gravel weigh?
This question seems circular, but it's asking about volume-to-weight relationship:
By definition: 1 ton of gravel = 2,000 pounds (that's what "ton" means)
But the real question is: How much volume (cubic yards)?
Volume equivalence:
- 1 ton of gravel ≈ 0.60-0.75 cubic yards (depending on gravel type and compaction)
- Loose gravel: 1 ton ≈ 0.75 cubic yards
- Compacted gravel: 1 ton ≈ 0.60 cubic yards
Reverse:
- 1 cubic yard of gravel ≈ 1.3-1.7 tons (2,600-3,400 lb depending on type)
Gravel types and density:
- Pea gravel: ~1.3 tons per cubic yard (lighter)
- Crushed stone: ~1.5 tons per cubic yard (typical)
- Dense granite: ~1.7 tons per cubic yard (heavier)
Practical example: If you need to cover a driveway area of 10 cubic yards, you'll need approximately 13-15 tons of gravel (10 yd³ × 1.3-1.5 tons/yd³).
What is the federal truck weight limit in tons?
The federal limit for trucks on interstate highways in the United States is:
80,000 pounds gross vehicle weight = 40 tons
This includes:
- Truck/tractor weight (tare weight)
- Trailer weight (tare weight)
- Cargo weight (payload)
- Fuel, driver, equipment
Axle limits:
- Single axle: 20,000 lb (10 tons) maximum
- Tandem axle: 34,000 lb (17 tons) maximum
- Total gross: 80,000 lb (40 tons) maximum
Bridge formula: The federal bridge formula determines allowable weight based on number of axles and spacing, which may further limit weight on shorter wheelbases.
State variations:
- Some states allow higher weights on specific routes (e.g., Michigan allows up to 164,000 lb / 82 tons with 11 axles)
- Permits: Overweight permits available for specialized hauling (heavy equipment, modular homes)
Violations: Fines for overweight trucks typically $0.10-$0.20 per pound over limit, escalating for serious violations.
How many tons can a dump truck carry?
Dump truck capacity varies by size and type:
Small dump trucks (single-axle):
- Payload: 5-8 tons (10,000-16,000 lb)
- Examples: Small commercial dumps, landscape trucks
- Typical load: 4-6 cubic yards material
Standard dump trucks (tandem-axle):
- Payload: 10-15 tons (20,000-30,000 lb)
- Examples: Construction dump trucks, municipal trucks
- Typical load: 8-12 cubic yards material
Tri-axle dump trucks:
- Payload: 15-18 tons (30,000-36,000 lb)
- Examples: Heavy construction, aggregate hauling
- Typical load: 12-15 cubic yards material
Transfer dump trucks (multi-axle):
- Payload: 20-26 tons (40,000-52,000 lb)
- Examples: Long combination vehicles, specialized hauling
- Typical load: 16-20 cubic yards material
Limitations:
- Federal limit: 80,000 lb (40 tons) gross vehicle weight
- Truck weight: Tare weight typically 15,000-30,000 lb (7.5-15 tons)
- Net payload: Actual cargo capacity = 40 tons minus truck weight
Material matters: Volume capacity depends on material density (sand ~1.5 tons/yd³, mulch ~0.4 tons/yd³).
What does "tonnage" mean in shipping?
In maritime shipping, "tonnage" can mean several different measurements:
1. Gross Tonnage (GT):
- Volume measurement of ship's entire internal space
- Not weight: Measured in "register tons" (100 cubic feet = 1 register ton)
- Usage: Ship classification, port fees, regulations
- Example: "Cargo ship: 50,000 GT"
2. Deadweight Tonnage (DWT):
- Weight measurement of cargo, fuel, crew, provisions ship can carry
- Actual weight capacity (what most people think of as "tonnage")
- Measured in: Metric tonnes (1,000 kg) internationally, sometimes US tons domestically
- Example: "Bulk carrier: 80,000 DWT" (can carry 80,000 tonnes cargo)
3. Displacement Tonnage:
- Total weight of ship (including ship structure + cargo + fuel + everything)
- Equals weight of water displaced by ship (Archimedes' principle)
- Usage: Naval vessels, ship design
- Example: "Aircraft carrier: 100,000 tons displacement"
4. Net Tonnage (NT):
- Volume of cargo spaces only (excludes engine room, crew quarters)
- Usage: Port fees, canal tolls (based on revenue-generating space)
Modern practice: International shipping primarily uses metric tonnes for weight measurements, while US domestic shipping may use US short tons.
About Atomic Mass Unit (u)
What is the value of 1 u (or Da) in kilograms?
Answer: 1 u = 1.660 539 066 60 × 10⁻²⁷ kg (with standard uncertainty ±0.000 000 000 50 × 10⁻²⁷ kg)
This extraordinarily precise value comes from measurements of carbon-12 atoms using mass spectrometry and relates to the newly defined kilogram (based on Planck's constant as of 2019).
Approximate value: 1 u ≈ 1.6605 × 10⁻²⁷ kg
In grams: 1 u ≈ 1.6605 × 10⁻²⁴ g
Memorization tip: "1.66 and exponent −27"
Uncertainty: The precision is about 0.3 parts per billion (extremely accurate!)
Source: CODATA 2018 recommended values (Committee on Data for Science and Technology)
Is the atomic mass unit (amu) the same as the Dalton (Da)?
Answer: Yes—in modern usage, u (unified atomic mass unit), amu, and Da (Dalton) all refer to the same unit
Historical context:
Pre-1961 (ambiguous):
- "amu" could mean the oxygen-based physics scale (¹⁶O = 16) or chemistry scale (natural O = 16)
- These differed by ~0.03%, causing confusion
1961 unification:
- IUPAC/IUPAP adopted carbon-12 standard
- "u" (unified atomic mass unit) replaced ambiguous "amu"
- 1 u = 1/12 mass of ¹²C atom
1970s-1993:
- "Dalton" (Da) proposed as an alternative name honoring John Dalton
- Gained popularity in biochemistry
Today:
- u: Official name, preferred in chemistry and physics
- Da: Alternative name, preferred in biochemistry (especially kDa for proteins)
- amu: Informal, but understood to mean "u" in modern contexts
Bottom line: 1 u = 1 Da = 1 amu (modern) — all identical
Why was Carbon-12 chosen as the standard for atomic mass?
Answer: Carbon-12 unified divergent physics and chemistry scales while being abundant, stable, and convenient
Historical problem (pre-1961):
- Physicists used ¹⁶O = 16.0000 exactly (pure isotope)
- Chemists used natural oxygen = 16.0000 exactly (isotope mixture)
- Natural oxygen is 99.757% ¹⁶O, 0.038% ¹⁷O, 0.205% ¹⁸O
- Result: Two incompatible atomic mass scales differing by ~0.03%
Carbon-12 advantages:
1. Unification: Resolved the physics-chemistry discrepancy with a single standard
2. Abundance: ¹²C comprises 98.89% of natural carbon (readily available)
3. Stability: Not radioactive (unlike ¹⁴C); doesn't decay
4. Integer mass: Defining ¹²C = 12 exactly gives a clean reference point
5. Chemical importance: Carbon is the basis of organic chemistry—central to life and synthetic compounds
6. Mass spectrometry: Carbon compounds are ubiquitous calibration standards
7. Convenience: Most atomic masses end up close to integers (approximately equal to mass number A)
Alternative considered: Hydrogen was Dalton's original choice, but hydrogen's mass (1.008 u) isn't exactly 1, and hydrogen forms fewer compounds than carbon or oxygen.
Result: Since 1961, all atomic weights worldwide are based on ¹²C = 12.0000 u (exact)
How does the atomic mass unit relate to Avogadro's number?
Answer: The atomic mass unit and Avogadro's number are defined such that mass in u equals molar mass in g/mol numerically
The elegant relationship:
Avogadro's constant: N_A = 6.022 140 76 × 10²³ mol⁻¹ (exact, as of 2019 SI redefinition)
Atomic mass unit: 1 u = 1/12 the mass of one ¹²C atom
Molar mass constant: M_u = 1 g/mol (by definition of the mole)
Mathematical relationship:
1 u = 1 g / N_A
Example:
- One carbon-12 atom: 12 u
- One mole of carbon-12 atoms: 12 g
- Number of atoms: 6.022 × 10²³
Practical consequence: To convert molecular mass (u) to grams, multiply by Avogadro's number:
- 1 water molecule: 18 u
- 1 mole of water: 18 g
- 18 g ÷ (6.022 × 10²³) = 2.99 × 10⁻²³ g per molecule ✓
Why this works: The definition of the mole (amount containing N_A entities) is coordinated with the definition of the atomic mass unit to make this numerical equality hold.
What is the difference between atomic mass and atomic weight?
Answer: Atomic mass refers to a specific isotope; atomic weight is the weighted average of all isotopes in natural abundance
Atomic mass (isotope-specific):
- Mass of one specific isotope
- Example: ¹²C has atomic mass = 12.0000 u (exact)
- Example: ¹³C has atomic mass = 13.0034 u
Atomic weight (element average):
- Weighted average of all naturally occurring isotopes
- Example: Natural carbon (98.89% ¹²C, 1.11% ¹³C) has atomic weight = 12.0107 u
- Listed on the periodic table
Calculation for carbon: Atomic weight = (0.9889 × 12.0000) + (0.0111 × 13.0034) = 12.0107 u
Why "weight" instead of "mass"? Historical naming; "atomic weight" actually refers to mass, not weight (force). The term persists despite being technically incorrect.
Relative atomic mass: Modern term preferred over "atomic weight" (same meaning, less confusing)
Important distinction: When doing precise isotope work (mass spectrometry, nuclear chemistry), use atomic masses of specific isotopes, not elemental atomic weights.
Can I use atomic mass units for objects larger than molecules?
Answer: Technically yes, but it's impractical—atomic mass units are too small for macroscopic objects
Practical range for atomic mass units:
- Atoms: 1-300 u (hydrogen to heaviest elements)
- Small molecules: 10-1,000 u
- Proteins: 1,000-10,000,000 u (1 kDa - 10 MDa)
- Viruses: up to ~1,000 MDa (1 gigadalton, GDa)
Beyond this: Use conventional mass units (grams, kilograms)
Example (why it's impractical):
- A grain of sand (~1 mg = 10⁻⁶ kg)
- In atomic mass units: 10⁻⁶ kg ÷ (1.66 × 10⁻²⁷ kg/u) ≈ 6 × 10²⁰ u
- This number is unwieldy!
Rule of thumb: Use atomic mass units for individual molecules or molecular complexes; switch to grams/kilograms for anything visible to the eye.
Extreme example: A 70 kg human = 4.2 × 10²⁸ u (42,000 trillion trillion u—utterly impractical!)
How accurate are modern atomic mass measurements?
Answer: Extraordinarily accurate—often 8-10 decimal places (parts per billion precision)
Modern mass spectrometry precision:
- Typical: 1 part per million (ppm) — 6 decimal places
- High-resolution: 1 part per billion (ppb) — 9 decimal places
- Ultra-high-resolution: 0.1 ppb — 10 decimal places
Example: Carbon-12:
- Defined as exactly 12.00000000000... u (infinite precision by definition)
Example: Hydrogen-1:
- Measured value: 1.00782503207 u (11 significant figures!)
- Uncertainty: ±0.00000000077 u
Why such precision matters:
1. Isotope identification: Distinguishing ¹²C¹H₄ (16.0313 u) from ¹³C¹H₃ (16.0344 u) requires high precision
2. Mass defect measurements: Nuclear binding energies calculated from tiny mass differences (0.1% of nuclear mass)
3. Molecular formula determination: Mass spectrometry can distinguish C₁₃H₁₂ from C₁₂H₁₂O from C₁₁H₁₆N (all ~168 u) with sufficient precision
4. Fundamental physics: Testing mass-energy equivalence, searching for physics beyond the Standard Model
Limitation: Even with extreme precision, natural isotopic variation (different ¹²C/¹³C ratios in different samples) limits practical accuracy to ~4-5 decimal places for most chemical applications.
Do protons and neutrons have exactly the same mass?
Answer: No—neutrons are slightly heavier than protons by about 0.14%
Precise values:
- Proton mass: 1.007276466621 u
- Neutron mass: 1.00866491595 u
- Difference: 0.00138845 u (neutron is heavier by ~1.4 MeV/c²)
Why this matters:
1. Neutron decay: Free neutrons decay into protons + electrons + antineutrinos with a half-life of ~10 minutes (neutron → proton + e⁻ + ν̄ₑ)
2. Nuclear stability: The mass difference affects which isotopes are stable vs. radioactive
3. Element synthesis: Mass differences determine which nuclear reactions can occur spontaneously in stars
Fun fact: Both are close to 1 u (within 1%), which is why atomic mass numbers (protons + neutrons) approximately equal atomic masses in u
Electron mass: Much lighter—only 0.000548580 u (~1/1836 of a proton)
Consequence: Atomic mass is almost entirely due to protons and neutrons; electrons contribute negligibly (<0.03%)
Why is the atomic mass of hydrogen 1.008 u instead of 1 u?
Answer: Because protons are slightly heavier than 1/12 of a carbon-12 atom, plus hydrogen atoms include an electron
Breakdown of hydrogen atom (¹H):
- Proton: 1.007276 u
- Electron: 0.000549 u
- Binding energy (negligible): −0.000015 u
- Total: 1.007825 u ≈ 1.008 u
Why isn't a proton exactly 1 u?
The atomic mass unit is defined as 1/12 the mass of carbon-12, which contains 6 protons + 6 neutrons + 6 electrons, minus the nuclear binding energy:
¹²C mass: 12 u (exact) = 6 protons + 6 neutrons + 6 electrons − binding energy
Solving: 1 nucleon (proton or neutron) ≈ 1.007-1.009 u (slightly more than 1 u)
Why the carbon-12 nucleus is lighter than 12 individual nucleons: Nuclear binding energy (E = mc²) converts ~0.1 u of mass into energy that holds the nucleus together
Result: Hydrogen (1 proton + 1 electron) ends up at 1.008 u, not 1.000 u
Will the definition of the atomic mass unit ever change?
Answer: Unlikely—the carbon-12 standard is stable, internationally accepted, and fundamental to chemistry
Why it's stable:
1. International agreement: IUPAC, IUPAP, and NIST all recognize ¹²C standard (since 1961)
2. Infrastructure: All atomic weight tables, databases, lab equipment calibrated to carbon-12
3. No compelling alternative: Carbon-12 works perfectly for chemistry and biochemistry
4. Historical continuity: Changing standards disrupts 60+ years of data
Recent change (2019 SI redefinition):
- The kilogram was redefined based on Planck's constant
- This indirectly affects the atomic mass unit (since 1 u is expressed in kg)
- But the change is at the 9th decimal place—completely negligible for chemistry
Future refinement: Values like 1.660539066(50) × 10⁻²⁷ kg will get more decimal places as measurements improve, but the carbon-12 definition (1 u = 1/12 m(¹²C)) won't change
Contrast with other standards:
- Meter: Redefined from physical bar to speed of light (1983)
- Kilogram: Redefined from physical cylinder to Planck constant (2019)
- Atomic mass unit: Based on fundamental particle (¹²C atom)—already a natural standard
Conclusion: The carbon-12 definition is here to stay for the foreseeable future (decades to centuries).
Conversion Table: Ton (US) to Atomic Mass Unit
| Ton (US) (ton) | Atomic Mass Unit (u) |
|---|---|
| 0.5 | 273,159,710,074,598,260,000,000,000,000 |
| 1 | 546,319,420,149,196,500,000,000,000,000 |
| 1.5 | 819,479,130,223,794,700,000,000,000,000 |
| 2 | 1,092,638,840,298,393,000,000,000,000,000 |
| 5 | 2,731,597,100,745,982,500,000,000,000,000 |
| 10 | 5,463,194,201,491,965,000,000,000,000,000 |
| 25 | 13,657,985,503,729,912,000,000,000,000,000 |
| 50 | 27,315,971,007,459,824,000,000,000,000,000 |
| 100 | 54,631,942,014,919,650,000,000,000,000,000 |
| 250 | 136,579,855,037,299,130,000,000,000,000,000 |
| 500 | 273,159,710,074,598,260,000,000,000,000,000 |
| 1,000 | 546,319,420,149,196,500,000,000,000,000,000 |
People Also Ask
How do I convert Ton (US) to Atomic Mass Unit?
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Learn more →What is the conversion factor from Ton (US) to Atomic Mass Unit?
The conversion factor depends on the specific relationship between Ton (US) and Atomic Mass Unit. You can find the exact conversion formula and factor on this page. Our calculator handles all calculations automatically. See the conversion table above for common values.
Can I convert Atomic Mass Unit back to Ton (US)?
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Learn more →What are common uses for Ton (US) and Atomic Mass Unit?
Ton (US) and Atomic Mass Unit are both standard units used in weight measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our weight converter for more conversion options.
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All conversion formulas have been verified against international standards and authoritative sources to ensure maximum accuracy and reliability.
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Last verified: December 3, 2025