Meter to Astronomical Unit Converter
Convert meters to astronomical units with our free online length converter.
Quick Answer
1 Meter = 6.684492e-12 astronomical units
Formula: Meter × conversion factor = Astronomical Unit
Use the calculator below for instant, accurate conversions.
Our Accuracy Guarantee
All conversion formulas on UnitsConverter.io have been verified against NIST (National Institute of Standards and Technology) guidelines and international SI standards. Our calculations are accurate to 10 decimal places for standard conversions and use arbitrary precision arithmetic for astronomical units.
Meter to Astronomical Unit Calculator
How to Use the Meter to Astronomical Unit Calculator:
- Enter the value you want to convert in the 'From' field (Meter).
- The converted value in Astronomical Unit will appear automatically in the 'To' field.
- Use the dropdown menus to select different units within the Length category.
- Click the swap button (⇌) to reverse the conversion direction.
How to Convert Meter to Astronomical Unit: Step-by-Step Guide
Converting Meter to Astronomical Unit involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Meter = 6.6845e-12 astronomical unitsExample Calculation:
Convert 10 meters: 10 × 6.6845e-12 = 6.6845e-11 astronomical 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.
Not for professional use. Results should be verified before use in any critical application. View our Terms of Service for more information.
Need to convert to other length units?
View all Length conversions →What is a Meter and a Astronomical Unit?
The meter (US spelling) or metre (International spelling) (symbol: m) is the base unit of length in the International System of Units (SI). It is one of the seven SI base units and forms the foundation for measuring distance in the metric system.
Modern Definition (1983): The meter is defined as the distance traveled by light in a vacuum in exactly 1/299,792,458 of a second. This definition links the meter to the speed of light, a fundamental constant of nature (c = 299,792,458 meters per second).
Key relationships:
- 1 meter = 100 centimeters (cm)
- 1 meter = 1,000 millimeters (mm)
- 1 meter = 0.001 kilometers (km)
- 1,000 meters = 1 kilometer
In terms of imperial/US customary units:
- 1 meter ≈ 3.28084 feet (ft) - Convert m to ft
- 1 meter ≈ 39.3701 inches (in) - Convert m to inches
- 1 meter ≈ 1.09361 yards (yd) - Convert m to yards
Visual perspective (how long is it?):
- 1 meter ≈ Length of a guitar
- 1 meter ≈ Distance from nose to fingertips (arm outstretched)
- 1 meter ≈ One adult step/stride
- 1 meter ≈ Width of a single bed
- 2 meters ≈ Standard doorway height
- 5 meters ≈ Length of a small car
It is the fundamental unit upon which all other SI length units are based through decimal multiplication or division.
Convert between length units: meter converter
1 astronomical unit (AU) = 149,597,870,700 meters (EXACT)
The astronomical unit is a unit of length in astronomy and planetary science, representing the mean distance from Earth to the Sun. Since 2012, the AU has been a defined constant—exactly 149,597,870,700 m—rather than a measured quantity.
Why Not Just Use Kilometers?
Scale problem: Solar System distances in kilometers become unwieldy:
- Earth to Sun: 149,597,871 km (hard to grasp)
- Jupiter to Sun: 778,500,000 km (increasingly meaningless)
- Neptune to Sun: 4,500,000,000 km (just a big number)
AU makes it intuitive:
- Earth: 1.00 AU (baseline)
- Jupiter: 5.20 AU (5× farther than Earth)
- Neptune: 30.1 AU (30× Earth's distance)
The human brain handles ratios better than absolute numbers. "Neptune is 30 times farther from the Sun than Earth" is far more comprehensible than "Neptune is 4.5 billion kilometers from the Sun."
Light Travel Time
The AU has a natural time component:
1 AU = 8 minutes 19 seconds at the speed of light
- Light from the Sun takes 8m 19s to reach Earth
- If the Sun suddenly vanished, we wouldn't know for 8+ minutes
- Solar flares and coronal mass ejections take this long to arrive
- Real-time communication with spacecraft: Earth-Mars = 4-24 minutes one-way delay (depending on orbital positions)
AU vs. Light-Year vs. Parsec
Three different distance scales for different contexts:
| Unit | Meters | Use Case | |----------|-----------|--------------| | Astronomical Unit (AU) | 1.496 × 10¹¹ m | Solar System (planets, asteroids, comets) | | Light-year (ly) | 9.461 × 10¹⁵ m (63,241 AU) | Interstellar distances (nearest stars) | | Parsec (pc) | 3.086 × 10¹⁶ m (206,265 AU) | Galactic/extragalactic distances (parallax-based) |
Why each exists:
- AU: Human-scale for our cosmic neighborhood
- Light-year: Intuitive (distance light travels in a year)
- Parsec: Technical (distance at which 1 AU subtends 1 arcsecond)
Note: The Meter is part of the metric (SI) system, primarily used globally in science and trade. The Astronomical Unit belongs to the imperial/US customary system.
History of the Meter and Astronomical Unit
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Pre-Revolutionary France (Pre-1790s): France used hundreds of different local length units, creating confusion in trade and science. The need for a universal, standardized system became critical.
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Birth of the Meter (1791-1793): During the French Revolution, the French Academy of Sciences proposed a new unit of length based on natural constants. They defined the meter as one ten-millionth (1/10,000,000) of the distance from the Earth's equator to the North Pole along the meridian passing through Paris.
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Meridian Survey (1792-1799): Astronomers Pierre Méchain and Jean-Baptiste Delambre conducted a seven-year expedition to measure the meridian arc from Dunkirk to Barcelona to determine the exact length of the meter. This ambitious survey became legendary in scientific history.
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Platinum Meter Bar (1799): Based on the meridian measurements, the first physical standard was created: a platinum bar stored in the French National Archives. This became the legal meter in France.
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Treaty of the Metre (1875): Seventeen nations signed this international treaty, establishing the General Conference on Weights and Measures (CGPM) and the International Bureau of Weights and Measures (BIPM) to maintain global measurement standards.
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International Prototype Meter (1889): A more precise platinum-iridium bar was created and designated as the international standard. This prototype was kept at the BIPM near Paris under controlled conditions (specific temperature, pressure, support points).
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Krypton-86 Definition (1960): To improve accuracy and reproducibility, the meter was redefined as 1,650,763.73 wavelengths of the orange-red light emitted by krypton-86 atoms in a vacuum. This was the first definition based on atomic physics rather than a physical object.
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Speed of Light Definition (1983): The current definition was adopted, fixing the speed of light at exactly 299,792,458 m/s and defining the meter based on this constant. This provided the most stable and reproducible definition possible, as the speed of light is a fundamental constant of nature.
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Global Adoption: Today, the meter is used by virtually every country in the world. Only Liberia, Myanmar, and the United States have not fully adopted the metric system for everyday use, though even the US uses it extensively in science, medicine, and manufacturing.
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Why It Matters: The meter's evolution from a physical bar to a definition based on universal constants represents humanity's quest for increasingly precise and universally accessible measurement standards.
Ancient Underestimates (300 BCE - 1500 CE)
Aristarchus of Samos (3rd century BCE): The first known attempt to measure the Earth-Sun distance. Using lunar phases and geometry, Aristarchus estimated the Sun was 18-20 times farther than the Moon. His method was sound, but observational limitations led to severe underestimation.
Actual ratio: Sun is ~400× farther than the Moon, not 20×.
Ptolemy's geocentric model (2nd century CE): Ptolemy's Almagest placed the Sun relatively close—around 1,200 Earth radii (~7.6 million km), about 5% of the true distance. This underestimation persisted for 1,400 years during the geocentric era.
Copernican Revolution (1543-1600s)
Nicolaus Copernicus (1543): De revolutionibus orbium coelestium established the heliocentric model. While Copernicus correctly ordered the planets, his distance estimates were still too small—placing the Sun about 20 million km away (13% of the actual distance).
Johannes Kepler (1609-1619): Kepler's laws of planetary motion (published in Astronomia Nova and Harmonices Mundi) enabled calculation of relative planetary distances. If Earth's orbit is 1 AU, then:
- Venus: 0.72 AU
- Mars: 1.52 AU
- Jupiter: 5.20 AU
Problem: Kepler knew the proportions, but not the absolute scale. What was the AU in meters or kilometers?
The Transit of Venus Method (1761-1769)
Edmond Halley's proposal (1716): Halley realized that observing Venus crossing the Sun's face (a "transit") from different Earth locations would create a parallax effect, enabling triangulation of the Earth-Sun distance.
1761 Transit of Venus: International expeditions to Siberia, South Africa, India, and the South Pacific. Observations were complicated by:
- The "black drop effect" (Venus appearing to stick to the Sun's edge)
- Cloudy weather disrupting measurements
- Imprecise timekeeping
1769 Transit of Venus: More extensive global coordination:
- Captain James Cook: Observed from Tahiti (Point Venus)
- Charles Mason & Jeremiah Dixon: Observed from the Cape of Good Hope
- Russian expeditions: Observed from Siberia
Result: Combined data yielded an Earth-Sun distance of approximately 153 million km, within 2% of the modern value (150M km). This was the first accurate measurement of the AU.
Why transits work: Observers at different latitudes see Venus cross the Sun along slightly different paths. The timing difference creates a parallax angle:
tan(parallax) = (Earth baseline) / (Earth-Sun distance)
With a known Earth baseline (distance between observation sites) and measured parallax, the AU could be calculated.
19th Century Refinement (1800-1900)
1874 and 1882 Transits of Venus: Equipped with photography and telegraph time-synchronization, astronomers improved AU measurements to ~149.5 million km.
Asteroid parallax (1898-1900): The asteroid 433 Eros passes closer to Earth than Venus, providing better parallax measurements. During Eros's 1900-1901 opposition, global observatories measured its position, refining the AU to 149.53 million km (±0.03%).
Term standardization: The phrase "astronomical unit" became standard in the late 19th century, replacing earlier terms like "solar distance" or "Earth's mean distance."
20th Century Precision (1961-2012)
Radar ranging to Venus (1961): The Goldstone Observatory and Jodrell Bank transmitted radar signals to Venus and measured the round-trip time. Since radio waves travel at the speed of light (c), the distance calculation was straightforward:
Distance = (c × round-trip time) / 2
Result: The AU was refined to 149,597,870 km (±1 km precision).
Radar ranging to Mars (1965-1976): Mariner and Viking spacecraft provided radar measurements, cross-verifying the Venus-based AU.
Viking landers (1976): Precise radio tracking of the Viking landers on Mars enabled AU measurements to sub-kilometer precision.
Jet Propulsion Laboratory ephemerides: JPL's Development Ephemeris (DE) models incorporated radar, spacecraft tracking, and lunar laser ranging. By 2000, the AU was known to meter-level precision.
IAU 2012 Redefinition
The problem: The AU was previously defined as "the radius of an unperturbed circular Newtonian orbit about the Sun of a particle having infinitesimal mass, moving with a mean motion of 0.01720209895 radians per day (the Gaussian gravitational constant)."
This definition was:
- Circular (tied to a theoretical model, not measurable)
- Dependent on the solar mass (which itself was measured in AU-based units)
- Subject to revision as measurements improved
The solution (IAU Resolution B2, 2012): The International Astronomical Union redefined the AU as a fixed constant:
1 AU = 149,597,870,700 meters (EXACT)
Why this matters:
- Consistency: The AU no longer changes with better measurements of solar mass
- Spacecraft navigation: JPL's navigation software uses this exact constant
- Parallels SI units: Like the meter (defined via the speed of light), the AU is now a defined standard, not a derived quantity
Fun fact: The chosen value (149,597,870,700 m) was the best measurement available in 2012, now frozen as the definition.
Cultural and Scientific Impact
The AU represents humanity's growing comprehension of cosmic scale:
- Ancient world: Sun thought to be ~10 million km away
- Kepler era: Relative distances known, absolute scale uncertain
- 1769: First accurate measurement (153M km, 2% error)
- 1961: Radar precision (±1 km)
- 2012: Defined as exact constant (no error—it IS the standard)
This progression mirrors the scientific method: hypothesis → observation → refinement → standardization.
Common Uses and Applications: meters vs astronomical units
Explore the typical applications for both Meter (metric) and Astronomical Unit (imperial/US) to understand their common contexts.
Common Uses for meters
The meter is the fundamental length unit used across virtually all fields worldwide:
Science and Research
The universal standard in all scientific disciplines. Essential for maintaining consistency in international research and allowing scientists globally to share and compare results.
Scientific Applications:
- Physics experiments and calculations
- Chemistry lab measurements
- Biology specimen measurements
- Astronomy (often combined with larger units like megameters or astronomical units)
- Geology and earth sciences
- Medical research and diagnostics
Why meters in science:
- SI base unit ensures universal understanding
- Decimal system simplifies calculations
- Precise definition based on fundamental constants
- Required for publication in scientific journals
- Enables international collaboration
Convert for scientific work: meters to other units
Construction and Engineering
Standard unit for building plans, specifications, and measurements in most countries. Essential for architectural drawings, structural engineering, and construction site work.
Construction uses:
- Building dimensions and floor plans
- Material specifications (lumber, pipes, cables)
- Site surveying and land measurements
- Road and bridge design
- Utility installations
- Safety clearances and regulations
Engineering disciplines:
- Civil engineering (infrastructure, roads, dams)
- Mechanical engineering (machine design, tolerances)
- Electrical engineering (cable runs, installations)
- Structural engineering (building analysis)
Why meters dominate:
- International building codes
- Global supply chains use metric
- Simplified scaling (1:100, 1:50 drawings)
- Easy conversion between units (mm, cm, m, km)
Athletics and Sports
The standard for track and field events, swimming pools, and most international sports. Creates consistency in competition and record-keeping worldwide.
Track and Field:
- All race distances (100m, 200m, 400m, etc.)
- Field event measurements (high jump, long jump, javelin)
- Track dimensions (400m oval)
Swimming:
- Pool lengths (25m, 50m)
- Race distances
- Pool depth specifications
Other Sports:
- Soccer field dimensions
- Basketball court measurements (FIBA)
- Tennis court specifications
- Ski jump distances
World Records: All Olympic and international records use meters
Manufacturing and Industry
Essential for product design, quality control, and manufacturing specifications. Enables global supply chains and standardized parts.
Manufacturing uses:
- Product dimensions and tolerances
- Machine specifications
- Assembly line measurements
- Quality control standards
- Shipping container sizes
- Material cutting and fabrication
Industries:
- Automotive (car dimensions, parts)
- Aerospace (aircraft specifications)
- Electronics (component spacing)
- Textiles (fabric measurements)
- Furniture (product dimensions)
Everyday Life (Metric Countries)
Daily measurements for height, distance, and dimensions in 95% of the world's countries.
Personal measurements:
- Human height and weight
- Clothing sizes (combined with cm)
- Recipe distances (rare, but when needed)
- Home improvement projects
Shopping:
- Fabric by the meter
- Carpeting and flooring
- Curtains and blinds
- Garden hoses and cables
Driving:
- Road signs (distances in km, using meters as base)
- Vehicle dimensions
- Parking regulations
Use our meter converter for everyday conversions.
Aviation and Maritime
Critical for navigation, altitude, and safety specifications in international travel.
Aviation:
- Runway lengths
- Aircraft dimensions
- Altitude (often in feet, but meters in some regions)
- Visibility distances
Maritime:
- Ship dimensions
- Harbor depths (often in meters or fathoms)
- Vessel clearances
- Navigation distances
Medical and Healthcare
Standard for patient measurements and medical equipment in most healthcare systems worldwide.
Medical uses:
- Patient height
- Wound measurements
- Medical imaging distances
- Equipment specifications
- Hospital room dimensions
- Surgical instrument lengths
When to Use astronomical units
1. Planetary Science and Orbital Mechanics
The AU is the natural unit for describing planetary orbits using Kepler's laws.
Kepler's Third Law:
P² = a³
Where:
- P = orbital period (Earth years)
- a = semi-major axis (AU)
Example: Mars
- Semi-major axis: 1.524 AU
- Predicted period: √(1.524³) = √(3.540) = 1.881 Earth years
- Actual period: 1.881 years (687 days) ✓
Why AU simplifies this: In SI units, Kepler's Third Law requires the gravitational constant G and solar mass M☉:
P² = (4π² / GM☉) × a³
Using AU and years, the constants vanish!
2. Asteroid and Comet Tracking
Orbital elements use AU:
- Semi-major axis (a): Average orbital distance (AU)
- Perihelion distance (q): Closest approach to Sun (AU)
- Aphelion distance (Q): Farthest point from Sun (AU)
Example: Halley's Comet
- Semi-major axis: 17.8 AU
- Perihelion: 0.586 AU (inside Venus's orbit)
- Aphelion: 35.1 AU (beyond Neptune)
- Orbital period: 75-76 years
Near-Earth Object (NEO) classification:
- Atens: Semi-major axis <1.0 AU, perihelion >0.983 AU
- Apollos: Semi-major axis >1.0 AU, perihelion <1.017 AU
- Amors: Semi-major axis >1.0 AU, perihelion 1.017-1.3 AU
3. Exoplanet Characterization
When astronomers discover exoplanets, they report orbital distances in AU for comparison with our Solar System.
Kepler-452b ("Earth's cousin"):
- Star: G-type (Sun-like)
- Distance from star: 1.05 AU
- Orbital period: 385 days
- Size: 1.6× Earth diameter
- In habitable zone (liquid water possible)
TRAPPIST-1 system:
- Star: Ultra-cool red dwarf (9% Sun's mass)
- 7 planets: 0.011 to 0.063 AU (all closer than Mercury!)
- 3 in habitable zone (TRAPPIST-1e, f, g)
- Why so close? Red dwarf is dim, HZ is much nearer
Proxima Centauri b:
- Distance from star: 0.0485 AU (7.3 million km)
- Orbital period: 11.2 days
- In habitable zone (red dwarf is faint)
- Nearest potentially habitable exoplanet (4.24 light-years)
4. Mission Planning and Spacecraft Navigation
Delta-v budgets: Spacecraft missions calculate fuel requirements based on AU distances.
Hohmann transfer orbit (Earth to Mars):
- Earth orbit: 1.00 AU (circular approximation)
- Mars orbit: 1.52 AU
- Transfer orbit semi-major axis: (1.00 + 1.52) / 2 = 1.26 AU
- Travel time: Half the transfer orbit period ≈ 259 days (8.5 months)
Launch windows: Earth and Mars align favorably every 26 months (synodic period). Missing a window means waiting 2+ years.
Example: Perseverance rover
- Launch: July 30, 2020
- Landing: February 18, 2021
- Distance traveled: ~480 million km (depends on orbital path, not straight-line)
5. Solar Wind and Space Weather
Heliosphere: The Sun's influence extends well beyond planetary orbits, measured in AU.
Termination shock: ~90 AU
- Solar wind slows below sound speed
- Voyager 1 crossed: 94 AU (2004)
Heliopause: ~120 AU
- Boundary where solar wind meets interstellar medium
- Voyager 1 crossed: 121 AU (2012)
Bow shock: ~150 AU
- Where interstellar medium piles up against heliosphere
Oort Cloud: 2,000-100,000 AU
- Spherical shell of icy comets surrounding Solar System
- Gravitationally bound to the Sun, but barely
6. Educational and Outreach
The AU provides an intuitive scale for teaching Solar System structure.
Scale models: If Earth = 1 cm diameter:
- Sun: 109 cm (1.09 m) diameter
- Earth-Sun distance: 117 m (1 AU scale)
- Jupiter: 11 cm diameter, 608 m from Sun
- Neptune: 4 cm diameter, 3.5 km from Sun!
The "Voyage" scale model (Washington, D.C.):
- 1:10 billion scale
- Sun (Smithsonian): 1.39 m diameter sphere
- Earth: 1.3 cm (grain of rice), 15 m away
- Pluto: 0.2 cm, 590 m away
7. Historical Astronomy
Pre-AU era challenges: Before the AU was accurately measured, astronomers knew relative planetary positions but not absolute distances.
Example: Kepler knew...
- Venus is 0.72× Earth's distance
- Mars is 1.52× Earth's distance
- Jupiter is 5.20× Earth's distance
...but NOT the actual Earth-Sun distance!
The AU filled this gap, providing the absolute scale.
Additional Unit Information
About Meter (m)
How long is a meter visually?
One meter is about the distance from your nose to your fingertips when you extend your arm straight out to the side.
Visual comparisons:
- Slightly longer than a yard (1 m = 1.09 yards)
- About 3.3 feet (one adult stride)
- Length of a guitar (most acoustic guitars)
- Width of a single bed
- Slightly longer than a baseball bat
- Three average-sized rulers (30cm each)
Body measurements:
- Most adults can approximate 1 meter with arm span from nose to fingertips
- One large step/stride for most adults
- Height from ground to waist/hip for average adult
Common objects exactly 1 meter:
- Meter stick/ruler (by definition)
- Certain guitar models
- Standard yoga mat width (60cm) is just over half a meter
To remember: Think of it as "just over 3 feet" or "slightly longer than a yard"
How many feet are in a meter?
One meter equals approximately 3.28084 feet, commonly rounded to 3.28 feet.
Exact conversion: 1 meter = 3.280839895 feet
Practical conversions:
- 1 meter ≈ 3.28 feet
- 2 meters ≈ 6.56 feet
- 5 meters ≈ 16.4 feet
- 10 meters ≈ 32.8 feet
- 100 meters ≈ 328 feet
Reverse conversion (feet to meters):
- 1 foot = 0.3048 meters (exactly)
- 3 feet ≈ 0.91 meters
- 6 feet ≈ 1.83 meters
- 10 feet ≈ 3.05 meters
Why 3.28?
- Based on the international foot definition (0.3048 m)
- 1 meter ÷ 0.3048 meters/foot = 3.28084 feet
Quick estimation: Multiply meters by 3 for a rough approximation (though this underestimates by ~9%)
Use our meter to feet converter for accurate conversions.
How many centimeters are in a meter?
There are exactly 100 centimeters (cm) in one meter.
Why 100?: The prefix "centi-" means 1/100, so a centimeter is 1/100 of a meter.
Conversion:
- 1 meter = 100 centimeters
- To convert meters to cm: multiply by 100
- To convert cm to meters: divide by 100
Examples:
- 0.5 meters = 50 cm
- 1.5 meters = 150 cm
- 2.75 meters = 275 cm
- 50 cm = 0.5 meters
- 175 cm = 1.75 meters (typical adult height)
Remember: Move the decimal point two places:
- Meters → cm: Move right (1.5 m = 150 cm)
- Cm → meters: Move left (150 cm = 1.5 m)
Use our meter to cm converter for instant conversions.
Is the meter used in the United States?
Officially: The US uses the metric system in science, medicine, military, and many industries, but the US customary system (feet, inches, miles) dominates everyday life.
Where meters ARE used in the US:
- Science and research: All scientific work
- Medicine: Patient measurements, medical devices
- Military: NATO standardization requires metric
- Manufacturing: Especially for export products
- Athletics: Track and field events
- Pharmaceuticals: Drug measurements
- Automotive: Many car specifications
- Electronics: Component specifications
Where meters are NOT commonly used:
- Road signs (miles, not kilometers)
- Construction (feet, inches)
- Everyday conversation (height, distance)
- Cooking (cups, ounces, not liters/grams)
- Real estate (square feet, acres)
- Weather (Fahrenheit, not Celsius)
Status: The US is officially metric (Metric Conversion Act of 1975) but implementation is voluntary, so dual systems coexist.
Fun fact: US money is metric (100 cents = 1 dollar), but most Americans don't think of it that way!
How many meters are in a kilometer?
There are exactly 1,000 meters in one kilometer.
Why: "Kilo-" is a Greek prefix meaning 1,000.
Conversion:
- 1 kilometer (km) = 1,000 meters (m)
- To convert km to m: multiply by 1,000
- To convert m to km: divide by 1,000
Examples:
- 0.5 km = 500 meters
- 1.5 km = 1,500 meters
- 2.5 km = 2,500 meters
- 5 km = 5,000 meters
- 10 km = 10,000 meters
- 500 m = 0.5 km
- 2,000 m = 2 km
Perspective:
- A kilometer is a common walking distance (10-15 minutes)
- 5K race = 5 kilometers = 5,000 meters
- Marathon = 42.195 kilometers = 42,195 meters
Remember: Move the decimal point three places:
- Km → m: Move right (1.5 km = 1,500 m)
- M → km: Move left (1,500 m = 1.5 km)
Convert: meters to kilometers | kilometers to meters
How is the meter defined today?
Current Definition (since 1983): The meter is defined as the distance light travels in a vacuum in exactly 1/299,792,458 of a second.
Why this definition?:
- Universal constant: The speed of light (c) is the same everywhere in the universe
- Extremely precise: Can be reproduced in any properly equipped laboratory
- No physical artifact: Doesn't depend on a prototype bar that could degrade
- Fundamentally stable: Based on physics, not human-made objects
What this means:
- The speed of light is fixed at exactly 299,792,458 meters per second
- This definition links length to time (which is measured even more precisely)
- Any lab with an atomic clock can reproduce the meter
Historical evolution:
- 1793: Earth meridian (1/10,000,000 of equator to pole)
- 1889: Platinum-iridium bar in Paris
- 1960: Krypton-86 wavelengths
- 1983: Speed of light (current definition)
Why it matters: This makes the meter one of the most precisely defined and reproducible units in all of science.
What's the difference between meter and metre?
No difference - they are the same unit, just different spellings!
Spelling variations:
- Meter: American English spelling (US, Philippines)
- Metre: International English spelling (UK, Canada, Australia, most other English-speaking countries)
Symbol: Both use m as the abbreviation
In practice:
- Scientific papers: Usually "metre" (international standard)
- US publications: Usually "meter"
- International Bureau (BIPM): Uses "metre"
- Both are 100% correct
Other metric units with dual spellings:
- Liter / Litre
- Centimeter / Centimetre
- Kilometer / Kilometre
Remember: The spelling doesn't affect the measurement - 1 meter = 1 metre = 1 m
How do you convert meters to inches?
To convert meters to inches, multiply by approximately 39.3701.
Conversion formula: inches = meters × 39.3701
Examples:
- 1 meter = 39.37 inches
- 2 meters = 78.74 inches
- 5 meters = 196.85 inches
- 0.5 meters = 19.69 inches
- 1.5 meters = 59.06 inches
Reverse conversion (inches to meters):
- 1 inch = 0.0254 meters (exactly)
- 12 inches (1 foot) = 0.3048 meters
- 36 inches (1 yard) = 0.9144 meters
Why 39.37?
- 1 meter = 100 cm
- 1 inch = 2.54 cm (exactly)
- 100 cm ÷ 2.54 cm/inch = 39.37 inches
Quick mental math:
- 1 meter ≈ 40 inches (close enough for rough estimates)
- 2.5 cm ≈ 1 inch, so 100 cm ≈ 40 inches
Use our meter to inches converter for precise conversions.
What is 2 meters in feet and inches?
2 meters = 6 feet 6.74 inches (or approximately 6 feet 7 inches)
Calculation:
- 2 meters = 6.56168 feet
- 6 full feet = 6 feet
- 0.56168 feet × 12 inches/foot = 6.74 inches
- Result: 6 feet 6.74 inches ≈ 6' 7"
Common 2-meter comparisons:
- Standard doorway height: 2-2.1 meters (6'7" - 6'11")
- Tall person height: 2 meters is very tall (99th percentile)
- Basketball player: Many NBA players are around 2 meters
- High jump bar: Elite athletes clear around 2 meters
Rounded conversions:
- 2.0 m = 6' 7"
- 2.1 m = 6' 11"
- 2.2 m = 7' 3"
Quick reference:
- 1.5 m = 4' 11"
- 1.8 m = 5' 11" (average adult male height)
- 2.0 m = 6' 7"
- 2.5 m = 8' 2"
Convert any height: meters to feet and inches
How many meters is a football field?
American Football:
- Playing field: 100 yards = 91.44 meters
- With end zones: 120 yards = 109.73 meters
- Width: 53.33 yards = 48.76 meters
Soccer/Football (International):
- Length: 100-110 meters (typical), 90-120 meters (FIFA rules)
- Width: 64-75 meters (typical), 45-90 meters (FIFA rules)
- Standard pitch: 105 × 68 meters
Common comparisons:
- 100 meters ≈ 1 American football field (length only, not counting end zones)
- 100 meters = 109.4 yards (9.4 yards longer than American football field)
- "100-meter dash" ≈ Length of American football field + 9 yards
Useful reference: "100 meters" is a standard way to visualize distance - slightly longer than an American football field.
Why is the meter important?
The meter is the foundation of the metric system, used by 95% of the world's population and essential for global science, trade, and communication.
Scientific importance:
- Base unit of SI system (international standard)
- Defined by fundamental constant (speed of light)
- Essential for all scientific research
- Enables global collaboration
Practical importance:
- Universal measurement standard
- Simplifies international trade
- Decimal-based (easy calculations)
- Used in manufacturing, construction, medicine
Global standardization:
- Ensures products fit across borders
- Aircraft, ships, vehicles have standard dimensions
- Medical equipment is universally compatible
- Scientific data can be shared internationally
Historical significance:
- Represents the Enlightenment ideal of universal standards
- First measurement based on nature (Earth meridian)
- Now based on fundamental physics (speed of light)
- Symbol of international cooperation
Modern life:
- GPS and navigation systems
- International sports records
- Global supply chains
- Scientific advancement
Bottom line: The meter makes global communication, commerce, and science possible.
About Astronomical Unit (AU)
1. Why use Astronomical Units instead of kilometers or miles?
Convenience and intuition.
Solar System distances in kilometers are unwieldy:
- Jupiter: 778,500,000 km from the Sun
- Neptune: 4,500,000,000 km
In AU:
- Jupiter: 5.20 AU
- Neptune: 30.1 AU
Human brains handle ratios better than large numbers. "Neptune is 30× farther from the Sun than Earth" is far more intuitive than "Neptune is 4.5 billion kilometers away."
Scientific advantage: Kepler's Third Law simplifies to P² = a³ when using AU and years, eliminating gravitational constants.
2. How many kilometers/miles is 1 AU?
Exactly 149,597,870.700 kilometers (since 2012 IAU definition).
Rounded values:
- Metric: ~150 million km (1.496 × 10⁸ km)
- Imperial: ~93 million miles (9.296 × 10⁷ mi)
Why "exactly"? As of 2012, the AU is a defined constant (like the speed of light), not a measured quantity. The meter is defined via the speed of light, and the AU is defined in meters, making it exact.
3. How long does it take light to travel 1 AU?
499.0 seconds = 8 minutes 19 seconds.
This is the "light travel time" from the Sun to Earth. When you see the Sun in the sky, you're seeing it as it was 8 minutes 19 seconds ago.
Implications:
- Solar flares take 8m 19s to reach Earth
- If the Sun vanished, we wouldn't know for 8+ minutes
- Real-time communication with Mars: 4-24 minute one-way delay
Formula:
Time = distance / speed of light
Time = 149,597,870,700 m / 299,792,458 m/s = 499.0 seconds
4. What is the difference between AU, light-year, and parsec?
Three distance units for different scales:
| Unit | Definition | Meters | Use Case | |----------|---------------|-----------|--------------| | AU | Earth-Sun distance | 1.496 × 10¹¹ m | Solar System (planets, asteroids) | | Light-year | Distance light travels in 1 year | 9.461 × 10¹⁵ m | Interstellar (nearest stars) | | Parsec | Distance where 1 AU subtends 1 arcsec | 3.086 × 10¹⁶ m | Galactic/extragalactic |
Conversions:
- 1 light-year = 63,241 AU
- 1 parsec = 206,265 AU = 3.26 light-years
Why each exists:
- AU: Intuitive for our cosmic neighborhood
- Light-year: Public-friendly (distance light travels in a year)
- Parsec: Technical (based on parallax measurements)
5. Why was the AU redefined in 2012?
To eliminate circular dependencies and fix the AU as a constant.
Old definition (pre-2012): The AU was tied to the Gaussian gravitational constant and solar mass, creating circular logic:
- Solar mass measured in kg using AU-based planetary orbits
- AU defined using solar mass
- Improved measurements of one changed the other
New definition (IAU 2012): 1 AU = 149,597,870,700 meters (EXACT)
Benefits:
- Consistency: The AU never changes, even with better solar mass measurements
- Spacecraft navigation: JPL navigation software uses this exact constant
- Parallels SI system: Like the meter (defined via speed of light), AU is now a defined standard
Fun fact: The chosen value was the best 2012 measurement, now frozen as the definition.
6. How far has Voyager 1 traveled in AU?
164 AU as of 2024 (24.5 billion km from the Sun).
Journey milestones:
- 1977: Launch from Earth (1 AU)
- 1979: Jupiter flyby (5.2 AU)
- 1980: Saturn flyby (9.5 AU)
- 2004: Crossed termination shock (94 AU) — solar wind slowed
- 2012: Entered interstellar space (121 AU) — crossed heliopause
- 2024: 164 AU and counting
Speed: 3.6 AU/year (17 km/s relative to the Sun)
Perspective:
- Voyager 1 has traveled 164× the Earth-Sun distance
- It's traveled only 0.0026 light-years (0.26% of a light-year)
- At this speed, it would take 75,000 years to reach Proxima Centauri (4.24 light-years)
7. What is the habitable zone in AU for our Solar System?
Approximately 0.95 to 1.37 AU for a Sun-like star.
Inner edge (0.95 AU): Too close → runaway greenhouse effect (like Venus at 0.72 AU)
- Water vapor traps heat
- Surface water evaporates
- Planet becomes uninhabitable
Outer edge (1.37 AU): Too far → frozen surface (Mars at 1.52 AU is marginal)
- Insufficient sunlight to maintain liquid water
- CO₂ freezes, reducing greenhouse warming
Earth (1.00 AU): Perfect!
- Liquid water oceans
- Temperate climate (greenhouse effect keeps average ~15°C)
Mars (1.52 AU): Marginal
- Thin atmosphere (lost over billions of years)
- Surface water frozen, but subsurface ice exists
- Past liquid water evidence (ancient river valleys)
Note: Habitable zone width depends on star type:
- Red dwarfs (dim): HZ is 0.05-0.15 AU
- Sun-like stars: HZ is 0.95-1.37 AU
- Blue giants: HZ is 10+ AU (but these stars don't live long enough for life to evolve)
8. How accurate is the AU measurement?
Perfectly accurate since 2012—it's a defined constant.
Pre-2012: The AU was measured using radar ranging, spacecraft tracking, and orbital mechanics. By 2000, precision reached sub-meter levels.
Post-2012: The IAU defined the AU as exactly 149,597,870,700 meters. This isn't a "measurement" anymore—it's the standard, like the meter is defined via the speed of light.
What this means:
- The AU has zero uncertainty (it's exact by definition)
- Measurements of planetary distances are now in meters, not AU
- The AU is a conversion factor (like 12 inches = 1 foot, exact)
9. Can you see 1 AU with the naked eye?
Yes! You're seeing across 1 AU whenever you look at the Sun.
What you're seeing:
- The Sun's surface is 1 AU away
- Sunlight takes 8 minutes 19 seconds to reach your eyes
- You're seeing the Sun as it was 8+ minutes ago
Other 1 AU experiences:
- Solar eclipses: Moon passes between Earth and Sun (~1 AU alignment)
- Sunlight warmth: Solar energy intensity at 1 AU is 1,361 W/m² (solar constant)
- Seasonal changes: Earth's 1 AU orbit, tilted 23.5°, creates seasons
10. How do astronomers measure AU distances?
Historically: Parallax, transits, and radar ranging. Now: The AU is a defined constant (not measured).
Historical methods:
1. Transits of Venus (1769): Observing Venus cross the Sun's face from different Earth locations enabled triangulation:
- Parallax angle measured
- Earth-Sun distance calculated: ~153 million km (2% error)
2. Radar ranging (1961+): Transmit radar to Venus/Mars, measure round-trip time:
Distance = (speed of light × round-trip time) / 2
Accuracy: Sub-kilometer precision
3. Spacecraft tracking (1976+): Viking landers on Mars, Voyager flybys, etc., provided precise radio ranging data.
Modern (2012+): The AU is defined as exactly 149,597,870,700 meters. Planetary distances are now measured in meters using spacecraft telemetry, and converted to AU using this exact constant.
11. Why don't we use AU for measuring distances to stars?
Because AU numbers become unwieldy for interstellar distances.
Example: Proxima Centauri (nearest star)
- Distance: 268,000 AU
- In light-years: 4.24 ly (much cleaner!)
It's like measuring New York to Tokyo in millimeters:
- 11 trillion millimeters (accurate but awkward)
- 11,000 kilometers (appropriate scale)
Astronomers do use AU for...
- Stellar parallax calculations (1 AU baseline enables distance measurements)
- Comparing exoplanet orbits to our Solar System
But for stellar distances:
- Light-years: Public-friendly, intuitive
- Parsecs: Professional astronomy (1 pc = 206,265 AU)
12. What is beyond 100 AU?
The edge of the Solar System and the beginning of interstellar space.
50-100 AU: Kuiper Belt
- Icy objects, dwarf planets (Pluto at 39.5 AU)
- Short-period comets originate here
90 AU: Termination Shock
- Solar wind slows below sound speed
120 AU: Heliopause
- Boundary where solar wind meets interstellar medium
- Voyager 1 crossed in 2012 (121 AU)
2,000-100,000 AU: Oort Cloud
- Spherical shell of icy comets
- Gravitationally bound to the Sun
- Long-period comets originate here
125,000 AU (~2 light-years): Sun's gravitational dominance ends
- Beyond this, nearby stars' gravity is comparable
- Practical edge of the Solar System
Perspective: Even at 100 AU, you're still deep within the Sun's influence. Interstellar space (between stars) begins around 100,000 AU.
Conversion Table: Meter to Astronomical Unit
| Meter (m) | Astronomical Unit (AU) |
|---|---|
| 0.5 | 0 |
| 1 | 0 |
| 1.5 | 0 |
| 2 | 0 |
| 5 | 0 |
| 10 | 0 |
| 25 | 0 |
| 50 | 0 |
| 100 | 0 |
| 250 | 0 |
| 500 | 0 |
| 1,000 | 0 |
People Also Ask
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The conversion factor depends on the specific relationship between Meter and Astronomical 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 Astronomical Unit back to Meter?
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Learn more →What are common uses for Meter and Astronomical Unit?
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Other Length Units and Conversions
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Last verified: December 3, 2025