Km to Miles Converter
Convert kilometers to miles — race distances, road signs, and trip odometers.
Updated
miles
6.21mi
10 km = 6.21 mi
In short
How many miles is 1 km?
One kilometer is 0.621371 miles, so divide kilometers by 1.609344 or multiply by 0.621371 to get miles. The 1.609344 is exact: the 1959 International Yard and Pound Agreement fixed the yard at 0.9144 meters, and a mile is 1,760 yards, so a mile is exactly 1,609.344 meters. 10 km is 6.21 miles.
The same factor converts speeds, so 100 kilometers per hour is 62.14 miles per hour with no extra arithmetic.
kilometers to miles — quick reference
| kilometers (km) | miles (mi) |
|---|---|
| 1 km | 0.62 mi |
| 5 km | 3.11 mi |
| 10 km | 6.21 mi |
| 21 km | 13.05 mi |
| 42 km | 26.10 mi |
| 50 km | 31.07 mi |
| 100 km | 62.14 mi |
| 200 km | 124.27 mi |
The formula, worked line by line
The mile is defined through the metric system, which is why this conversion is exact rather than approximate. The International Yard and Pound Agreement signed on 1 July 1959 by the United States, the United Kingdom, Canada, Australia, New Zealand and South Africa fixed the yard at exactly 0.9144 meters. A statute mile is 1,760 yards, so a mile is exactly 1,609.344 meters, or 1.609344 kilometers. The foot follows as exactly 0.3048 meters and the inch as exactly 25.4 millimeters.
So kilometers to miles is a division by an exact constant, equivalently a multiplication by its reciprocal, 0.6213711922 and onwards. Speeds use the same factor, because kilometers per hour and miles per hour share the same time unit; only the length changes. That is why one number does double duty for both a distance sign and a speed-limit sign.
miles = kilometers ÷ 1.609344
= kilometers × 0.62137119…
mph = (km/h) ÷ 1.609344
10 km → 10 ÷ 1.609344 = 6.213712 mi- Kilometers entered
- 10
- Exact divisor
- 1.609344 km per mile
- Division
- 10 ÷ 1.609344 = 6.2137119
- Miles
- 6.21 mi
The marathon is where the exactness pays off. World Athletics standardized the distance in 1921 at 42.195 km, taken from the 1908 London Olympic course of 26 miles 385 yards, which is itself exactly 42,194.988 meters. Convert the standard: 42.195 ÷ 1.609344 = 26.218757 miles. That is where the famous 26.2 comes from, and it is a rounding of a metric number rather than a target in its own right.
Read it: The shortfall is about 3.44 percent everywhere and always low, and on a 500 km drive it is enough to change a decision about a fuel stop. The five-eighths version, multiply by 5 and divide by 8, is much better: it gives 0.625 against the true 0.621371, an error of 0.58 percent on the high side, so 500 km reads as 312.5 miles against a true 310.69.
If you are going to memorize one shortcut, memorize five-eighths, and remember it reads long rather than short.
The other miles
Two other miles exist and neither is this one. The international nautical mile, used in aviation, marine navigation and territorial-water law, was defined at the 1929 hydrographic conference in Monaco as exactly 1,852 meters, which is 1.15078 statute miles, so a speed in knots is about 15 percent higher than the same number in mph.
And in the United States there was a survey mile, built from the US survey foot of 1200/3937 meters, which ran about two parts per million longer than the international mile, roughly an eighth of an inch per mile. NIST and the National Geodetic Survey deprecated the US survey foot on 31 December 2022, so from 1 January 2023 US practice has a single foot and a single mile.
How to use the km to miles converter
Kilometers reach US readers through a few specific doors. A race billed as a 10K, the road signs and speed limits on a trip abroad, the distance a foreign map app quotes, the odometer on a rental car set to metric, an activity tracker whose default was never changed, a cycling route shared by someone in Europe.
This converter turns kilometers into miles you can feel, and Swap handles the reverse when you are the one entering miles. The tool divides by 1.609344, the exact number of kilometers in a statute mile, rather than multiplying by a rounded 0.62, so the answer holds up over a 500 km drive as well as a 5 km run. What follows is where the difference between exact and roughly right actually shows up.
31.07 mph
50 km/h
the common built-up limit abroad
62.14 mph
100 km/h
80.78 mph
130 km/h
the fastest common motorway limit
Driving abroad is where the conversion affects decisions in real time, because you are reading a sign at speed. A sign showing 120 km to the next city means 74.56 miles. Speed limits convert with the same factor: 50 km/h is 31.07 mph, 80 km/h is 49.71 mph, 100 km/h is 62.14 mph, 110 km/h is 68.35 mph, and 130 km/h is 80.78 mph.
The mental shortcut most people use is multiplying kilometers by 0.6, which is good enough for reading a road sign. It runs about 3.4 percent low, so 10 km reads as 6 against a true 6.21 and 100 km reads as 60 against a true 62.14.
If you want something better that is still easy, multiply by 5 and divide by 8: that is 0.625, only 0.58 percent high, so 100 km gives 62.5 against a true 62.14.
Either version is fine for planning a run or judging whether you will make the next exit. Switch to the exact factor when a distance is billed, logged, or officially measured, and particularly when it is going to be multiplied by something else, such as a per-mile rate.
The distances people actually race and ride, each shown in both units, so you can see which are round in kilometers and which are round in miles. The metric-round rows are the officially defined ones; the mile-round rows are the American event distances.
| Distance | Kilometers | Miles |
|---|---|---|
| One lap of a standard outdoor track (400 m) | 0.4 km | 0.24855 mi |
| 1,500 m, the metric mile | 1.5 km | 0.93206 mi |
| One statute mile | 1.609344 km | 1 mi |
| 5K | 5 km | 3.10686 mi |
| 10K | 10 km | 6.21371 mi |
| 15K | 15 km | 9.32057 mi |
| Ten miles | 16.09344 km | 10 mi |
| Half marathon | 21.0975 km | 13.10938 mi |
| Marathon | 42.195 km | 26.21876 mi |
| 50K ultramarathon | 50 km | 31.06856 mi |
| Fifty miles | 80.4672 km | 50 mi |
| Metric century | 100 km | 62.13712 mi |
| One hundred miles | 160.9344 km | 100 mi |
Race distances: metric first, miles after
Running and cycling are the everyday case, and it helps to know that road racing was standardized in metric from the start. A 5K is 3.10686 miles, a 10K is 6.21371 miles, and a metric century of 100 km is 62.13712 miles.
If you train in miles and race a metric course, that matters for pacing: a 4-minute-per-kilometer pace is a 6:26 mile, and a 6-minute mile is a 3:44 kilometer, so a plan written in one unit does not transfer by eye.
Training in miles for a metric race
If your watch logs miles and the entry form wants kilometers, converting your own long runs is what stops a plan written in one unit from coming up short.
Open the miles to km converter →Every kilometers value, worked out
73 common kilometers figures each get their own page, with the answer at full precision, the arithmetic, what rounding costs, and the nearest real-world reference point on the scale.
Questions people ask
Sources
Where the constants and formulas on this page come from. Each line names the figure it backs.
The international mile is defined as exactly 1609.344 metres.
NIST Guide to the SI, Appendix B.8 — Factors for units listed alphabetically — NIST
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