Whether you're reading a race distance, a foreign speed limit, or a car's odometer, converting kilometers to miles comes up constantly. The exact factor is simple, and a rough version is easy to do in your head. Here's the formula, a full chart, and the shortcut.
The exact conversion factor
One kilometer equals 0.621371 miles. To convert kilometers to miles, multiply by 0.621371. To go the other way, multiply miles by 1.609344 to get kilometers. These factors come from the definition of the international mile as exactly 1,609.344 metres.
KM to miles quick reference chart
Common distances rounded to two decimals, including the standard running races:
| Kilometers | Miles |
|---|---|
| 1 km | 0.62 mi |
| 5 km | 3.11 mi |
| 10 km | 6.21 mi |
| 21.1 km (half marathon) | 13.11 mi |
| 42.2 km (marathon) | 26.22 mi |
| 50 km | 31.07 mi |
| 100 km | 62.14 mi |
How to convert km to miles in your head
For a fast estimate, multiply by 0.6 — close enough for most everyday purposes. So 100 km/h is roughly 60 mph (the exact value is 62), and a 10 km run is about 6 miles. For a slightly better approximation, multiply by 0.62. The mental shortcut is least accurate at large distances, where the missing 0.021 per km adds up, so reach for the exact factor when precision matters.
Why kilometers and miles both exist
The kilometer is part of the metric system (SI), built on powers of ten and used by most of the world. The mile is an imperial unit with Roman roots — the Latin mille passuum, "a thousand paces." The United States, and the UK for road signs, still use miles day to day, while science, athletics, and most other countries use kilometers. That split is why conversion is a constant traveling companion.
Where you'll use this
- Running: 5K and 10K races are in kilometers; US runners often think in miles (3.1 and 6.2).
- Road trips: foreign distance signs and rental-car odometers may be in kilometers.
- Speed limits: 50 km/h ≈ 31 mph, 100 km/h ≈ 62 mph, 120 km/h ≈ 75 mph.
- Fitness apps and treadmills that let you switch units mid-workout.
Need pace as well as distance? See what pace you need for a sub-2-hour half marathon.
How to convert miles back to kilometers
Going the other way, multiply miles by 1.609344 to get kilometers. So a 26.2-mile marathon is 26.2 × 1.609344 = 42.2 km, and a 60 mph speed limit is about 97 km/h. For a mental estimate, multiply miles by 1.6 — a 5-mile run is roughly 8 km. The two factors are reciprocals: 0.621371 and 1.609344 multiply to 1, which is why one undoes the other.
Where the conversion factor comes from
Since 1959, the international mile has been defined as exactly 1,609.344 metres — that's 1.609344 kilometers. Divide one by the other and you get 0.621371 miles per kilometer. Because the definition is exact, these conversion factors are exact too; the only rounding is whatever you choose to apply to the final answer. The older US survey mile differs by a few millimeters per mile and matters only for large-scale land surveying, not everyday distances.
Common speed conversions
Speeds convert with the same factor — km/h to mph is still × 0.621371:
| km/h | mph |
|---|---|
| 30 km/h | 18.6 mph |
| 50 km/h | 31.1 mph |
| 80 km/h | 49.7 mph |
| 100 km/h | 62.1 mph |
| 120 km/h | 74.6 mph |
Why the 0.6 shortcut drifts
Multiplying by 0.6 is quick but always undershoots, because the true factor is 0.621371. The error is about 3.4% — small for short distances (a 5 km run estimated at 3 miles is really 3.11) but meaningful over long ones (100 km estimated at 60 miles is really 62.1, a two-mile gap). Use 0.6 for a rough sense of scale and the exact factor whenever the number matters, such as fuel economy, race results, or navigation.
A note for runners switching units
Many training plans and treadmills let you flip between units mid-session, which is where people get tripped up. The key race distances are worth memorizing: a 5K is 3.1 miles, a 10K is 6.2 miles, a half marathon (21.1 km) is 13.1 miles, and a marathon (42.2 km) is 26.2 miles. Pace converts too — a 5:00/km pace is about 8:03/mile. If you think in one unit but race in the other, keep a chart handy or convert once before you start.
Is a 5K or a 5-mile race longer?
A 5-mile race is longer. A 5K is 5 kilometers, which is 3.11 miles — so a 5-mile race (8.05 km) is over 60% farther. This trips people up because the numbers look similar. The same applies to a 10K (6.21 miles) versus a 10-mile race (16.09 km): the 10-mile event is more than half again as long. When you sign up for a race, check whether the distance is in kilometers or miles before you plan your pace, because mistaking one for the other can mean training for the wrong distance entirely.