Kilometer to Angstrom Converter
Convert kilometers to angstroms with our free online length converter.
Quick Answer
1 Kilometer = 1.000000e+13 angstroms
Formula: Kilometer × conversion factor = Angstrom
Use the calculator below for instant, accurate conversions.
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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.
Kilometer to Angstrom Calculator
How to Use the Kilometer to Angstrom Calculator:
- Enter the value you want to convert in the 'From' field (Kilometer).
- The converted value in Angstrom 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 Kilometer to Angstrom: Step-by-Step Guide
Converting Kilometer to Angstrom involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Kilometer = 1.0000e+13 angstromsExample Calculation:
Convert 10 kilometers: 10 × 1.0000e+13 = 1.0000e+14 angstroms
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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Need to convert to other length units?
View all Length conversions →What is a Kilometer and a Angstrom?
The kilometer is a unit of length in the International System of Units (SI), the modern form of the metric system. One kilometer equals exactly 1,000 meters by definition, making it a straightforward decimal multiple of the base SI length unit.
The kilometer is denoted by the symbol km (lowercase 'k', lowercase 'm'). The spelling varies by region: "kilometre" in British English and Commonwealth countries, "kilometer" in American English, though both refer to the same measurement.
The kilometer represents the standard distance unit for:
- Road distances and highway signage worldwide (except USA, Myanmar, Liberia)
- Geographic features: city separation, coastline length, river length
- Transportation: vehicle range, fuel efficiency (km/L or L/100km)
- Athletics: running and cycling race distances (5K, 10K, marathon)
- Aviation: visibility distances, some altitude references in certain countries
The metric system's decimal structure makes kilometer conversions simple:
- 1 kilometer = 1,000 meters (exactly)
- 1 kilometer = 100,000 centimeters
- 1 kilometer = 1,000,000 millimeters
- 1 meter = 0.001 kilometers
- 1 centimeter = 0.00001 kilometers
The Angstrom (symbol Å) is a non-SI unit of length equal to exactly 10⁻¹⁰ meters (one ten-billionth of a meter) or 0.1 nanometers (nm). While not part of the modern International System of Units (SI), it remains widely used in various scientific fields due to its convenient scale for atomic and molecular dimensions.
The Angstrom provides a direct way to express sizes at the sub-nanometer level without resorting to fractions or powers of ten. For example, expressing a carbon-carbon bond as "1.54 Å" is more intuitive than "0.154 nm" or "154 pm" for scientists working at the atomic scale.
Relationship to other units:
- 1 Angstrom = 0.1 nanometers (nm)
- 1 Angstrom = 100 picometers (pm)
- 1 Angstrom = 0.0001 micrometers (μm)
- 10 Angstroms = 1 nanometer
- 10 billion Angstroms = 1 meter
Special character note: The proper symbol is Å (capital A with a ring above), not simply "A". This distinguishes it from amperes (A) and other uses of the letter A in scientific notation.
Convert Angstroms to Other Units →
Note: The Kilometer is part of the metric (SI) system, primarily used globally in science and trade. The Angstrom belongs to the imperial/US customary system.
History of the Kilometer and Angstrom
The kilometer emerged during one of history's most ambitious standardization efforts—the creation of the metric system during the French Revolution.
Metric System Origins (1790s): In 1791, the French Academy of Sciences proposed a universal measurement system based on natural constants rather than arbitrary royal decrees. They defined the meter as one ten-millionth of the distance from the North Pole to the equator along the Paris meridian. For longer distances, they created the kilometer (from Greek khilioi = thousand, plus metron = measure).
Decimal Simplicity: Unlike traditional systems with complex conversions (5,280 feet per mile, 1,760 yards per mile), the metric system used consistent decimal relationships. This made the kilometer instantly comprehensible: 1 km = 1,000 m, with no fractional arithmetic required.
Global Adoption: The metric system spread rapidly throughout Europe in the early 1800s. Napoleon's conquests carried metric measurements across the continent. By the mid-19th century, most European nations had officially adopted kilometers for distance measurement.
International Treaty (1875): The Metre Convention, signed by 17 nations, established the International Bureau of Weights and Measures (BIPM) and made the metric system the international scientific standard. Kilometers became the globally recognized unit for geographic and travel distances.
Road Sign Conversion: Through the 20th century, country after country converted road signage from miles to kilometers:
- Germany: 1920s (early adopter)
- Japan: 1924
- France: Kilometers used since metric system creation (1795)
- Australia: 1974 (major conversion effort)
- Canada: 1977 (gradual conversion)
- United Kingdom: Still uses miles despite metric adoption elsewhere
- Ireland: 2005 (one of the last European conversions)
Modern Definition (1983): The meter was redefined based on the speed of light: the distance light travels in vacuum during 1/299,792,458 of a second. This made the kilometer precisely 299,792,458/299,792,458,000 of the distance light travels in one second, tying it to a fundamental physical constant rather than a physical artifact.
Global Standard: Today, approximately 195 of 198 countries use kilometers as their primary road distance measurement. Only the United States, Myanmar, and Liberia officially use miles, though Myanmar is gradually transitioning to metric. The kilometer has become effectively universal for international travel, trade, and communication.
The Angstrom unit is named after the Swedish physicist Anders Jonas Ångström (1814–1874), one of the founders of the science of spectroscopy. Ångström made groundbreaking contributions to understanding electromagnetic radiation and atomic emission spectra.
In 1868, Ångström published a chart of the solar spectrum, expressing the wavelengths of electromagnetic radiation in sunlight as multiples of 10⁻¹⁰ meters. This scale proved extraordinarily convenient for expressing:
- Atomic radii (typically 0.5-3 Å)
- Chemical bond lengths (typically 1-2 Å)
- Wavelengths of X-rays (1-10 Å)
- Crystal lattice spacings (2-10 Å)
The Angstrom quickly became the standard unit in crystallography, chemistry, and atomic physics throughout the early 20th century. X-ray crystallography, developed by Max von Laue, William Henry Bragg, and William Lawrence Bragg in the 1910s, relied heavily on Angstrom measurements for determining crystal structures.
When the International System of Units (SI) was established in 1960, the Angstrom was officially deprecated in favor of:
- Nanometer (nm) = 10⁻⁹ m (preferred for 0.1-100 nm scales)
- Picometer (pm) = 10⁻¹² m (preferred for atomic-scale measurements)
Despite this official change, the Angstrom persists robustly in scientific literature for several reasons:
- Historical data: Decades of crystallography and spectroscopy literature use Angstroms
- Convenient scale: Atomic dimensions typically fall in the 0.5-5 Å range—easy to work with
- Established conventions: Many scientific fields developed their nomenclature around Angstroms
- Software and databases: Crystallographic databases (PDB, CIF) often default to Angstroms
Today, you will find Angstroms in:
- Protein Data Bank (PDB) files for biomolecular structures
- X-ray diffraction data and crystallographic information files (CIF)
- Chemistry textbooks for bond lengths and atomic radii
- Materials science publications for thin film thickness and surface studies
Learn More About Scientific Units →
Common Uses and Applications: kilometers vs angstroms
Explore the typical applications for both Kilometer (metric) and Angstrom (imperial/US) to understand their common contexts.
Common Uses for kilometers
International Road Travel and GPS
GPS navigation systems worldwide default to kilometers in metric countries. Drivers receive instructions like "In 2 kilometers, turn left" or "Your destination is 45 kilometers away." Trip computers display "distance to empty" in kilometers, helping drivers plan fuel stops.
Road atlases and mapping applications show distance scales in kilometers. Drivers estimate travel time using kilometers: "It's 300 km, so at 100 km/h average, that's 3 hours of driving" becomes intuitive mental math.
Highway interchanges number by kilometer markers in many countries. "Exit 245" means the exit is 245 km from the highway's starting point, making distance calculation simple: the gap between Exit 245 and Exit 310 is 65 km.
Public Transportation and Urban Transit
Metro, train, and bus systems describe route lengths and network extent in kilometers:
Urban Rail Systems:
- Tokyo Metro: 304 km of track, 179 stations
- London Underground: 402 km of track
- New York City Subway: 380 km of track
- Paris Métro: 226 km of track
High-Speed Rail:
- China high-speed network: 40,000+ km (world's largest)
- Europe high-speed: 11,000+ km network
- Japan Shinkansen: 3,000+ km
- Trains operate at 250-350 km/h
Commuters describe their journey: "I take the train 35 km to work" or "The metro line is 25 km end to end."
Logistics and Freight
Shipping companies calculate costs, routes, and delivery times in kilometers:
Trucking:
- Per-kilometer rates: €0.50-2.00 per km depending on cargo
- Driver limits: 500-900 km daily maximum (varying by regulations)
- Route optimization: Software minimizes total kilometers driven
Delivery Services:
- Local delivery: 0-50 km radius
- Regional delivery: 50-200 km
- National delivery: 200-1,000+ km
Supply Chain: "Warehouse is 150 km from port" or "Distribution center serves 200 km radius" inform logistics planning and inventory positioning.
Scientific and Environmental Research
Scientific studies report distances in kilometers:
Climate Science:
- Ice shelf extent: "Antarctic ice shelf extends 500 km from coast"
- Glacier retreat: "Glacier receded 5 km over past decade"
- Ocean currents: "Gulf Stream flows 10,000 km across Atlantic"
Geology:
- Fault lines: "San Andreas Fault extends 1,200 km through California"
- Volcanic reach: "Ash cloud spread 500 km from eruption"
Ecology:
- Animal migration: "Caribou migrate 5,000 km annually"
- Bird migration: "Arctic terns migrate 70,000 km round trip"
Sports and Recreation
Beyond running, many sports use kilometer measurements:
Hiking:
- Day hike: 5-20 km round trip
- Multi-day trek: 10-30 km per day
- Long-distance trails: Appalachian Trail 3,500 km, Pacific Crest Trail 4,300 km
Swimming:
- Open water races: 5 km, 10 km, 25 km
- English Channel: 34 km minimum straight-line distance (actual swim 40-50 km due to currents)
Skiing:
- Cross-country ski race: 10 km, 30 km, 50 km distances
- Ski resort terrain: "Resort has 150 km of marked runs"
Sailing:
- Yacht races: Sydney to Hobart 1,170 km, Volvo Ocean Race circumnavigates 72,000+ km
Agriculture and Land Management
Farms and land parcels measure in hectares, with distances in kilometers:
Farm Infrastructure:
- Irrigation canal: 10-50 km length serving agricultural region
- Fence line: "Property has 15 km of fencing"
- Farm roads: "30 km of internal roads"
Rural Distances:
- "Town is 25 km away"
- "Nearest hospital 60 km"
- "Property borders 2 km of river frontage"
Real Estate and Property
Property descriptions include kilometer proximity to amenities:
Location Descriptions:
- "5 km to city center"
- "2 km to nearest school"
- "15 km to international airport"
- "Within 1 km of public transport"
Commute Distance: Property values often correlate with kilometer distance from employment centers. "Within 10 km of downtown" commands premium pricing compared to "40 km from city center."
Emergency Services
Police, fire, and ambulance services track response distances and coverage areas in kilometers:
Response Zones:
- Ambulance coverage: Aim for < 8 km from any location
- Fire station spacing: 3-5 km apart in urban areas
- Police patrol areas: Officers cover 10-30 km² sectors
Response Times: "Average response time 8 minutes for locations within 5 km of station" guides emergency service planning.
Telecommunications and Utilities
Infrastructure planners measure network reach and service areas in kilometers:
Power Distribution:
- High-voltage transmission: Hundreds to thousands of km
- Distribution lines: 5-20 km from substation to customers
- Rural electrification: "Extended power 50 km to remote village"
Water Supply:
- Aqueduct: "200 km pipeline from reservoir to city"
- Distribution network: "City has 2,000 km of water mains"
Internet Infrastructure:
- "Fiber backbone runs 5,000 km across country"
- "Last-mile connections within 3 km of exchange"
When to Use angstroms
1. Crystallography
Crystallographers use Angstroms as the standard unit for crystal structure determination via X-ray, neutron, or electron diffraction. The spacing between atomic planes (d-spacings) in crystals typically ranges from 1-10 Å, making the Angstrom the natural unit. Crystallographic Information Files (CIF) and crystallography software default to Angstrom units.
Convert Crystal Measurements →
2. Atomic and Molecular Physics
Physicists measuring atomic radii, ionic radii, and atomic orbital sizes use Angstroms because typical atomic dimensions fall in the 0.5-5 Å range. Quantum mechanics calculations often output electron densities and orbital sizes in Angstroms for convenient interpretation.
3. Chemistry and Bond Lengths
Chemists specify molecular structures with bond lengths in Angstroms. Chemical databases, molecular modeling software, and computational chemistry programs (like Gaussian, ORCA, and VASP) typically use Angstrom coordinates. This convention allows for easy comparison across decades of chemical literature.
Calculate Molecular Dimensions →
4. Structural Biology
Protein crystallography and cryo-electron microscopy (cryo-EM) express protein structures in Angstroms. The Protein Data Bank (PDB)—the worldwide repository of 3D biological macromolecular structures—uses Angstroms as the standard coordinate unit. Resolutions of protein structures are also reported in Angstroms (e.g., "2.5 Å resolution").
Convert Protein Measurements →
5. X-ray Spectroscopy
X-ray wavelengths naturally fall in the 0.1-100 Å range, making Angstroms the convenient unit for X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and synchrotron radiation experiments. Energy-dispersive X-ray spectroscopy (EDS) also references wavelengths in Angstroms.
6. Thin Film Technology
Materials scientists characterize thin films, coatings, and surface layers in Angstroms, particularly for films thinner than 100 Å (10 nm). Atomic layer deposition (ALD), molecular beam epitaxy (MBE), and physical vapor deposition (PVD) processes often specify thicknesses in Angstroms for precision.
7. Surface Science
Surface scientists studying adsorption, catalysis, and surface reconstruction use Angstroms to measure adsorbate heights, surface step heights (typically 2-4 Å), and interlayer spacings. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) data are often expressed in Angstroms vertically.
Additional Unit Information
About Kilometer (km)
How many meters are in a kilometer?
There are exactly 1,000 meters in 1 kilometer. This relationship is definitional—the prefix "kilo-" means 1,000 in the metric system.
Converting kilometers to meters: Multiply by 1,000
- 1 km = 1,000 m
- 2.5 km = 2,500 m
- 0.5 km = 500 m
- 10 km = 10,000 m
Converting meters to kilometers: Divide by 1,000
- 1,500 m = 1.5 km
- 5,000 m = 5 km
- 500 m = 0.5 km
- 42,195 m = 42.195 km (marathon distance)
The metric system's decimal structure makes these conversions simple—just move the decimal point three places.
How many kilometers are in a mile?
One mile equals exactly 1.609344 kilometers. This conversion factor was established through the 1959 international yard and pound agreement, which defined the yard (and thus the mile) in terms of meters.
Quick conversions:
- 1 mile = 1.609 km
- 5 miles = 8.047 km
- 10 miles = 16.093 km
- 26.2 miles (marathon) = 42.195 km
Reverse conversion: 1 kilometer = 0.621371 miles
- 1 km ≈ 0.62 miles (about 5/8 of a mile)
- 5 km = 3.107 miles
- 10 km = 6.214 miles
- 100 km = 62.137 miles
Mental approximation: For rough estimates, remember "5 miles ≈ 8 km" or "8 km ≈ 5 miles." This Fibonacci-pair approximation gives about 1% accuracy and is easy to remember. More roughly, "1 mile ≈ 1.6 km" works for casual conversion.
What does 'kilo' mean in kilometer?
The prefix "kilo-" means one thousand (1,000). It derives from the Greek word khilioi, meaning thousand.
In the metric system, "kilo-" consistently indicates multiplication by 1,000:
- 1 kilometer (km) = 1,000 meters
- 1 kilogram (kg) = 1,000 grams
- 1 kiloliter (kL) = 1,000 liters
- 1 kilobyte (kB) = 1,000 bytes (in decimal notation)
- 1 kilowatt (kW) = 1,000 watts
This consistent prefix system makes the metric system easy to learn. Once you know "kilo = 1,000," you can understand any kilo- measurement immediately.
Other common metric prefixes:
- Mega- (M) = 1,000,000 (million)
- Kilo- (k) = 1,000 (thousand)
- Hecto- (h) = 100 (hundred)
- Deca- (da) = 10 (ten)
- Deci- (d) = 0.1 (tenth)
- Centi- (c) = 0.01 (hundredth)
- Milli- (m) = 0.001 (thousandth)
Is a kilometer longer or shorter than a mile?
A kilometer is shorter than a mile. One mile equals approximately 1.61 kilometers, making a mile about 61% longer than a kilometer.
Comparison:
- 1 mile = 1.609344 km
- 1 km = 0.621371 miles
Practical comparison:
- 5K race = 3.11 miles (shorter than 5 miles)
- 10K race = 6.21 miles (shorter than 10 miles)
- 100 km = 62.1 miles (significantly shorter than 100 miles)
Mental shortcut: Think "kilometers are smaller, so you need more of them." To cover the same distance:
- 100 miles requires 161 kilometers
- 100 kilometers equals only 62 miles
This difference matters when traveling internationally. A road sign showing "Paris 100 km" means about 62 miles—much closer than "100 miles" would be. Speed limits work the same way: "100 km/h" equals about 62 mph, considerably slower than "100 mph."
Why does most of the world use kilometers instead of miles?
Approximately 195 of 198 countries use kilometers because the metric system is simpler, more logical, and internationally standardized. Only the United States, Myanmar, and Liberia officially use miles, with Myanmar gradually transitioning to metric.
Decimal Simplicity: The metric system uses consistent base-10 relationships:
- 1 km = 1,000 m (easy conversion)
- Compare to: 1 mile = 1,760 yards = 5,280 feet (complex conversion)
Children in metric countries learn one simple rule: move the decimal point. American children must memorize: 12 inches per foot, 3 feet per yard, 1,760 yards per mile.
International Trade: The Metre Convention (1875) established metric as the international scientific and commercial standard. Countries adopting metric gained advantages in international trade, scientific collaboration, and technical documentation.
Post-Colonial Transitions: Former British colonies gradually converted from imperial to metric:
- Australia: 1970s
- Canada: 1970s-1980s (though some imperial usage persists)
- India: 1950s-1960s
- South Africa: 1970s
Only the United Kingdom retained miles for road signage despite otherwise adopting metric.
US Resistance: America resisted conversion due to:
- Massive infrastructure costs (replacing millions of road signs)
- Public opposition (polls show Americans prefer familiar units)
- No perceived benefit justifying disruption and expense
- "Metric Conversion Act" of 1975 made metric voluntary, not mandatory
Scientific Reality: Even the US uses metric in science, medicine, and military. The paradox: US scientists publish in metric while consumers shop in imperial.
How do you convert speed from mph to km/h?
To convert miles per hour (mph) to kilometers per hour (km/h), multiply by 1.609344. This gives exact results.
Formula: km/h = mph × 1.609344
Common speed conversions:
- 30 mph = 48.3 km/h (urban speed limit)
- 55 mph = 88.5 km/h (rural highway)
- 60 mph = 96.6 km/h (≈100 km/h common highway limit)
- 70 mph = 112.7 km/h
- 75 mph = 120.7 km/h
- 80 mph = 128.7 km/h
Reverse conversion (km/h to mph): Divide by 1.609344, or multiply by 0.621371
- 50 km/h = 31.1 mph (urban limit in metric countries)
- 90 km/h = 55.9 mph (rural road)
- 100 km/h = 62.1 mph (common highway limit)
- 110 km/h = 68.3 mph
- 120 km/h = 74.6 mph
- 130 km/h = 80.8 mph (German autobahn advisory speed)
Mental approximation: Multiply mph by 1.6 for quick estimates:
- 60 mph × 1.6 ≈ 96 km/h (actual: 96.6, very close)
- 70 mph × 1.6 ≈ 112 km/h (actual: 112.7, very close)
Or divide km/h by 1.6 for reverse estimate:
- 100 km/h ÷ 1.6 ≈ 62.5 mph (actual: 62.1, close enough)
Why it matters: Tourists driving in foreign countries must convert speed limits mentally to avoid speeding tickets. Rental cars may show speedometers in only one unit, requiring constant mental conversion.
What's the difference between km and km²?
Kilometers (km) measure linear distance in one dimension—how far apart two points are, or how long something stretches.
Square kilometers (km²) measure area in two dimensions—how much surface space something covers.
Linear distance (km):
- Road distance: "Paris is 100 km from here"
- Running race: "10 km race"
- River length: "Danube River is 2,850 km long"
- Border: "3,000 km border with neighboring country"
Area (km²):
- City size: "Paris covers 105 km²"
- Country size: "France has an area of 640,000 km²"
- Lake surface: "Lake Geneva covers 580 km²"
- Forest: "National park protects 1,200 km² of wilderness"
The math:
- Multiplying two distances creates area: 10 km × 5 km = 50 km²
- 1 km² = 1,000,000 m² = 100 hectares
- A square with 1 km sides has area of 1 km²
- A square with 10 km sides has area of 100 km² (not 10 km!)
Common confusion: "The city is 50 km" is incomplete—50 km in which direction? Better: "The city center is 50 km away" (linear distance) or "The city covers 200 km²" (area).
How far is a 5K race in miles?
A 5K race is 3.107 miles. The "K" in "5K" stands for kilometers, so 5K means 5 kilometers.
Exact conversion: 5 km × 0.621371 miles/km = 3.10686 miles ≈ 3.11 miles
For practical purposes: 5K ≈ 3.1 miles (slightly over 3 miles)
Common running distances:
- 5K: 5 km = 3.11 miles (popular beginner race distance)
- 10K: 10 km = 6.21 miles (popular intermediate distance)
- 15K: 15 km = 9.32 miles
- Half-marathon: 21.0975 km = 13.11 miles (exactly half of marathon)
- Marathon: 42.195 km = 26.219 miles
- 50K: 50 km = 31.07 miles (ultramarathon)
- 100K: 100 km = 62.14 miles (ultramarathon)
Why "K" notation? Running races worldwide use kilometer distances even in countries that otherwise use miles (like the US). This creates universal race standards—a 5K is the same distance whether run in New York, Paris, or Tokyo. The "K" abbreviation became standard running terminology.
Pace conversion: A runner completing 5K in 25 minutes averages:
- 5:00 per kilometer (25 minutes ÷ 5 km)
- 8:03 per mile (25 minutes ÷ 3.107 miles)
How do you calculate distance on a map with a kilometer scale?
Map scales show how many kilometers in the real world correspond to a unit distance on the map. Common map scales for road maps use kilometers.
Common scale notations:
- 1:100,000 means 1 cm on map = 100,000 cm (1 km) in reality
- 1:250,000 means 1 cm on map = 250,000 cm (2.5 km) in reality
- 1:50,000 means 1 cm on map = 50,000 cm (0.5 km or 500 m) in reality
Using the graphic scale: Most maps include a graphic scale bar showing distances directly:
|——————|
0 50 100 km
Measuring distance:
- Use a ruler or string to measure the map distance
- Compare to the scale bar or use the ratio
- Calculate actual distance
Example: On a 1:100,000 scale map:
- Measure 5 cm between two cities
- 5 cm × 1 km/cm = 5 km actual distance
For curved routes (roads, rivers): Lay a string along the curved path, then measure the string length against the scale.
Digital maps: Online mapping tools calculate distances automatically, displaying both kilometers and miles. Google Maps, for instance, shows "15 km" or "9.3 mi" depending on regional settings.
What's the origin of the marathon distance 42.195 kilometers?
The marathon distance of 42.195 kilometers (26 miles, 385 yards) has a fascinating history combining ancient legend with modern royal preference.
Ancient Legend: The marathon commemorates the run of Greek soldier Pheidippides, who allegedly ran from the Battle of Marathon to Athens (about 40 km) to announce victory over Persia in 490 BCE, then died from exhaustion. This legend inspired the modern marathon race.
Original Olympic Distance (1896-1908): Early Olympic marathons varied in distance, roughly 40 km but not standardized. Different Olympic marathons measured 40 km (1896 Athens), 40.26 km (1900 Paris), 41.86 km (1904 St. Louis), 40 km (1906 Athens).
1908 London Olympics—The Defining Race: The modern distance was set for the 1908 London Olympics. The race began at Windsor Castle and finished at the Olympic Stadium. Originally planned as 26 miles, an extra 385 yards was added so the race would finish directly in front of the royal box where Queen Alexandra sat.
Total distance: 26 miles + 385 yards = 26.219 miles = 42.195 kilometers
Standardization (1921): The International Amateur Athletic Federation (IAAF) officially adopted 42.195 km as the standard marathon distance in 1921, codifying the 1908 London course distance for all future marathons.
Modern Usage: Every certified marathon worldwide measures exactly 42.195 kilometers (or 26 miles 385 yards). Famous marathons—Boston, New York City, London, Berlin, Tokyo—all use this precise distance. Race courses must be certified to ensure accuracy, typically measured using calibrated bicycle wheels.
Half-Marathon: Exactly half of 42.195 km = 21.0975 km (13.1 miles), also standardized for half-marathon races worldwide.
About Angstrom (Å)
How many Angstroms are in a meter?
There are 10,000,000,000 (ten billion) Angstroms in one meter (1 m = 10¹⁰ Å). Conversely, 1 Angstrom = 10⁻¹⁰ meters.
To visualize this enormous number: if you lined up 10 billion atoms side by side (each about 1 Å in radius), they would span approximately 1 meter.
Examples:
- 1 meter = 10,000,000,000 Å
- 1 millimeter = 10,000,000 Å
- 1 micrometer = 10,000 Å
- 1 nanometer = 10 Å
How many Angstroms are in a nanometer?
There are exactly 10 Angstroms (Å) in one nanometer (nm). Therefore, 1 Å = 0.1 nm.
This 10:1 ratio makes conversions straightforward:
- 1 nm = 10 Å
- 5 nm = 50 Å
- 0.5 nm = 5 Å
- 0.15 nm = 1.5 Å
Memory trick: Think "A nanometer is 10 Angstroms" (the number 10 is hidden in "ten").
Convert Angstroms to Nanometers →
Is the Angstrom an SI unit?
No, the Angstrom is not part of the International System of Units (SI). The official SI unit for length at this scale is:
- Nanometer (nm) = 10⁻⁹ m (for 0.1-1000 nm scales)
- Picometer (pm) = 10⁻¹² m (for atomic-scale measurements)
Relationship: 1 Å = 0.1 nm = 100 pm
The SI system officially deprecated the Angstrom in 1960, but it remains widely used in crystallography, chemistry, and physics due to historical convention and its convenient scale for atomic dimensions.
Why is the Angstrom still used if it is not an SI unit?
The Angstrom persists due to:
1. Historical Convention: Decades of scientific literature (1868-present) use Angstroms. Converting all historical data would be impractical.
2. Convenient Scale: Atomic radii typically range from 0.5-3 Å—easy whole numbers. In nanometers, these become 0.05-0.3 nm (more decimal places).
3. Established Databases: Major scientific databases default to Angstroms:
- Protein Data Bank (PDB): all coordinates in Angstroms
- Crystallographic Information Files (CIF): lattice parameters in Angstroms
- Chemical structure databases: bond lengths in Angstroms
4. Software Defaults: Most crystallography and molecular modeling software uses Angstroms as the default unit.
5. Intuitive Communication: Saying "1.5 Angstroms" is often clearer than "150 picometers" or "0.15 nanometers" in research discussions.
What fields commonly use Angstroms?
The Angstrom remains common in:
Primary fields:
- Crystallography: X-ray, neutron, and electron diffraction for crystal structure determination
- Structural Biology: Protein and nucleic acid structure determination (PDB files)
- Chemistry: Molecular geometry, bond lengths, and computational chemistry
- Atomic Physics: Atomic radii, orbital sizes, and spectroscopy
Secondary fields:
- Materials Science: Thin films, surface science, and nanostructures
- Spectroscopy: X-ray wavelengths and absorption spectra
- Microscopy: Electron microscopy and scanning probe microscopy
- Semiconductor Physics: Historical or informal references to feature sizes
Compare Different Scientific Units →
How do you type the Angstrom symbol (Å)?
Typing the proper Angstrom symbol Å varies by platform:
Windows:
- Hold Alt and type 0197 on numeric keypad: Å
- Or use Character Map application
Mac:
- Option + Shift + A: Å
Linux:
- Compose key + A + A: Å
- Or Ctrl + Shift + U, then type 00C5, then Enter
HTML/Web:
- HTML entity:
Å→ Å - Unicode:
Å→ Å
LaTeX:
\AAor\r{A}→ Å
Microsoft Word:
- Insert → Symbol → select Å
- Or AutoCorrect: type (A) and it may convert automatically
If the symbol is unavailable, write "Angstrom" or abbreviate as "Ang" in informal contexts.
What is the difference between Angstrom and picometer?
An Angstrom (Å) equals 10⁻¹⁰ meters, while a picometer (pm) equals 10⁻¹² meters. This means 1 Angstrom = 100 picometers.
Scale comparison:
- Angstrom scale: atomic radii, bond lengths (0.5-5 Å = 50-500 pm)
- Picometer scale: ultra-precise bond length measurements, nuclear radii
Examples:
- Hydrogen atom radius: 0.53 Å = 53 pm
- C-H bond length: 1.09 Å = 109 pm
- C-C single bond: 1.54 Å = 154 pm
Usage differences:
- Angstroms: Traditional in chemistry and crystallography (though not SI-compliant)
- Picometers: Official SI unit, required by some journals and standards bodies
Many scientists prefer Angstroms for convenience (whole numbers), while formal SI publications require picometers or nanometers.
Convert Angstroms to Picometers →
How is Angstrom used in protein crystallography?
In protein crystallography, the Angstrom is the standard unit for:
1. Atomic Coordinates: PDB files list x, y, z coordinates of every atom in Angstroms.
2. Resolution: The quality of diffraction data is expressed in Angstroms:
- High resolution: <1.5 Å (individual atoms clearly visible)
- Medium resolution: 1.5-3.0 Å (backbone and side chains visible)
- Low resolution: >3.0 Å (overall fold visible, details limited)
3. Bond Lengths: Standard bond lengths used for structure refinement:
- C-C: 1.54 Å
- C-N: 1.47 Å
- C-O: 1.43 Å
4. Crystal Lattice: Unit cell dimensions (a, b, c axes) are given in Angstroms, typically 50-200 Å.
5. B-factors: Atomic displacement parameters are in Ų (square Angstroms).
Example: "The structure was solved at 2.1 Å resolution with unit cell dimensions a=62.3 Å, b=78.5 Å, c=91.2 Å."
Convert Crystallography Units →
Can I convert Angstroms to inches?
Yes, but it is extremely impractical. Angstroms measure atomic scales, while inches measure everyday objects—a difference of 10 billion!
Conversion: 1 Angstrom = 3.937 × 10⁻⁹ inches (about 0.000000004 inches)
Or inversely: 1 inch = 254,000,000 Å (254 million Angstroms)
Example: A carbon atom with radius 0.77 Å = 0.000000003 inches. This is why scientists use metric units—Angstroms, nanometers, and picometers are far more practical for atomic-scale work.
Convert Angstroms to Practical Units →
Why is it called Angstrom and not Ångström?
The English spelling "Angstrom" is a simplified version of the Swedish name "Ångström" to accommodate keyboards and alphabets without special characters.
Proper Swedish spelling: Anders Jonas Ångström (with the Swedish letter "Å")
Common variations:
- Angstrom (English, without diacritics)
- Ångström (Swedish/original spelling)
- Ångstrom (mixed form)
All refer to the same unit and the same physicist. The symbol Å remains universal across languages, representing both the unit and the first letter of Ångström's name (with the ring above).
In scientific writing, either "Angstrom" or "Ångström" is acceptable, though the simplified "Angstrom" is more common in English-language publications.
Conversion Table: Kilometer to Angstrom
| Kilometer (km) | Angstrom (Å) |
|---|---|
| 0.5 | 5,000,000,000,000 |
| 1 | 10,000,000,000,000 |
| 1.5 | 15,000,000,000,000 |
| 2 | 20,000,000,000,000 |
| 5 | 50,000,000,000,000 |
| 10 | 100,000,000,000,000 |
| 25 | 250,000,000,000,000 |
| 50 | 500,000,000,000,000 |
| 100 | 1,000,000,000,000,000 |
| 250 | 2,500,000,000,000,000 |
| 500 | 5,000,000,000,000,000 |
| 1,000 | 10,000,000,000,000,000 |
People Also Ask
How do I convert Kilometer to Angstrom?
To convert Kilometer to Angstrom, enter the value in Kilometer in the calculator above. The conversion will happen automatically. Use our free online converter for instant and accurate results. You can also visit our length converter page to convert between other units in this category.
Learn more →What is the conversion factor from Kilometer to Angstrom?
The conversion factor depends on the specific relationship between Kilometer and Angstrom. 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 Angstrom back to Kilometer?
Yes! You can easily convert Angstrom back to Kilometer by using the swap button (⇌) in the calculator above, or by visiting our Angstrom to Kilometer converter page. You can also explore other length conversions on our category page.
Learn more →What are common uses for Kilometer and Angstrom?
Kilometer and Angstrom are both standard units used in length measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our length converter for more conversion options.
For more length conversion questions, visit our FAQ page or explore our conversion guides.
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Other Length Units and Conversions
Explore other length units and their conversion options:
- Meter (m) • Kilometer to Meter
- Hectometer (hm) • Kilometer to Hectometer
- Decimeter (dm) • Kilometer to Decimeter
- Centimeter (cm) • Kilometer to Centimeter
- Millimeter (mm) • Kilometer to Millimeter
- Inch (in) • Kilometer to Inch
- Foot (ft) • Kilometer to Foot
- Yard (yd) • Kilometer to Yard
- Mile (mi) • Kilometer to Mile
- Nautical Mile (NM) • Kilometer to Nautical Mile
Verified Against Authority Standards
All conversion formulas have been verified against international standards and authoritative sources to ensure maximum accuracy and reliability.
National Institute of Standards and Technology — Official US standards for length measurements
Bureau International des Poids et Mesures — International System of Units official documentation
Last verified: December 3, 2025