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Kilometers to miles, converted instantly
Enter a distance in kilometers and this calculator returns the equivalent in miles. Useful for travellers, runners, cyclists, and anyone moving between metric and imperial countries.
The formula
To convert kilometers to miles, multiply by 0.621371:
miles = km × 0.621371
- miles — the result in statute miles.
- km — the input distance in kilometers.
- 0.621371 — derived from the exact definition: 1 mile = 1,609.344 m, so 1 km = 1,000 ÷ 1,609.344 miles.
The reverse: to convert miles to km, multiply by 1.609344 (see the Miles to KM calculator).
Worked example
Using the default input of 10 km:
- Multiply by the conversion factor: 10 × 0.621371 = 6.21371…
- Round to 4 decimal places: 6.2137 miles.
So 10 km ≈ 6.2137 miles. This is a well-known benchmark — a 10 km running race is just over 6.2 miles.
KM to miles reference table
| Kilometers | Miles |
|---|---|
| 1 km | 0.6214 mi |
| 5 km | 3.1069 mi |
| 10 km | 6.2137 mi |
| 21.1 km | 13.109 mi (half marathon) |
| 25 km | 15.534 mi |
| 42.2 km | 26.219 mi (marathon) |
| 50 km | 31.069 mi |
| 100 km | 62.137 mi |
| 200 km | 124.27 mi |
| 500 km | 310.69 mi |
| 1,000 km | 621.37 mi |
History & standards
The kilometre is an SI unit equal to 1,000 metres. The metre itself was redefined in 1983 by the BIPM as the distance light travels in a vacuum in 1/299,792,458 of a second — an exact, reproducible physical constant.
The mile is an imperial/US customary unit fixed by the 1959 International Yard and Pound Agreement at exactly 1,609.344 metres. This single agreement underpins every km-to-miles calculation: 1 km = 1,000 ÷ 1,609.344 = 0.621371… miles.
Most of the world uses kilometres for road distances, speed limits, and GPS coordinates. The main holdouts using miles are the United States, United Kingdom, and a handful of territories. Even the UK uses km/h on motorway variable-speed signs and metric in all scientific contexts.
Common applications
- Running races. Standard distances (5 km, 10 km, half marathon 21.1 km, marathon 42.2 km) are defined in kilometers but often quoted in miles for US audiences.
- Road trips. European GPS and road signs show km; US maps show miles. Converting helps you compare journey times.
- Cycling. Most cycling computers can display either unit; knowing the exact factor avoids confusion on mixed-unit routes.
- Car speedometers. Imported vehicles may have a second dial in km/h or mph; knowing the distance factor helps verify odometer readings.
Limitations & gotchas
- This calculator converts statute (land) miles. A nautical mile = 1.852 km exactly — do not use this tool for sea charts or aviation waypoints.
- The conversion factor 0.621371 is rounded. For maximum precision the unrounded value is 0.6213711922… (non-terminating decimal).
- Country-specific “miles” (e.g. the Irish mile of 2,048 m historically) are not the same as the modern statute mile. Always verify context.
Sources & references
- BIPM, “The International System of Units (SI), 9th edition” (2019).
- NIST Special Publication 330 (2019).
- 1959 International Yard and Pound Agreement, Federal Register.
FAQs
5 km × 0.621371 = 3.107 miles. The 5 km distance is a very common running race distance; knowing it equals about 3.1 miles helps pace yourself on mixed-unit courses.
Close but not quite. The exact conversion is 1 km = 0.621371 miles. Rounding to 0.6 gives a 3.5% underestimate, which is fine for rough mental arithmetic but too imprecise for navigation or race timing.
Multiply km by 0.6 for a quick estimate, then add about 3.5% of that figure for a closer result. A popular shortcut used by cyclists: divide by 8 and multiply by 5. For example, 80 km ÷ 8 = 10; 10 × 5 = 50 miles (exact: 49.71 miles) — within 1%.
The UK never fully converted road signs to metric. A 1970 plan to switch was shelved due to cost. Today, UK road signs show miles and yards; speed limits are in mph. However, UK medicine, science, and most consumer packaging use metric (km, m, kg). The result is a hybrid system unique to Britain.
100 km = 62.137 miles. This is also the approximate distance of a 100 km ultramarathon, which takes elite runners around 6–7 hours. At motorway speed (100 km/h or 62 mph), this distance takes exactly one hour.
The exact factor is 0.621371192… miles per kilometre, which derives from the 1959 definition: 1 mile = 1,609.344 m exactly. Therefore 1 km = 1,000 ÷ 1,609.344 = 0.6213711922… miles. For most purposes, 0.621371 is sufficient.