Drive from the United States into Canada and the road signs switch from miles to kilometers at the border. The UK uses miles and miles per hour on its roads, but runs 5K and 10K races in kilometers. Knowing how to move between the two quickly helps with speed limits, travel plans and training.
The exact relationship
The international mile is defined as exactly 1,609.344 meters, so:
| Unit | Equals |
|---|---|
| 1 mile (mi) | 1.609344 km, exactly |
| 1 kilometer (km) | 0.621371 mi (rounded) |
| 1 nautical mile | 1.852 km, exactly (used at sea and in aviation) |
Formulas
miles = kilometers × 0.621371
kilometers = miles × 1.609344
Worked example: 250 km × 0.621371 = 155.3 miles, roughly the drive from London to Manchester.
Worked example: 26.2 miles × 1.609344 = 42.2 km, the marathon distance.
Two shortcuts you can do in your head
Multiply by 0.6 and add a little. 80 km × 0.6 = 48, and the exact answer is 49.7 miles. Adding 3% to the 0.6 result gets you within a fraction of a mile.
The Fibonacci trick. Neighbouring numbers in the Fibonacci sequence (2, 3, 5, 8, 13, 21, 34, 55, 89...) have a ratio close to 1.6, which is almost the km-per-mile figure. So:
- 5 miles ≈ 8 km
- 8 miles ≈ 13 km
- 13 miles ≈ 21 km
- 55 miles ≈ 89 km
For numbers that are not in the sequence, split them into Fibonacci numbers: 100 km = 89 + 8 + 3, which gives 55 + 5 + 2 = 62 miles (exact: 62.14).
Speed: mph and km/h
The same factor converts speeds:
- mph = km/h × 0.621371
- km/h = mph × 1.609344
| km/h | mph | mph | km/h | |
|---|---|---|---|---|
| 30 km/h | 18.6 mph | 20 mph | 32.2 km/h | |
| 50 km/h | 31.1 mph | 30 mph | 48.3 km/h | |
| 80 km/h | 49.7 mph | 50 mph | 80.5 km/h | |
| 100 km/h | 62.1 mph | 60 mph | 96.6 km/h | |
| 110 km/h | 68.4 mph | 70 mph | 112.7 km/h | |
| 120 km/h | 74.6 mph | 80 mph | 128.7 km/h |
Note: speed limits are set by law and change. Typical figures are 70 mph on UK motorways, 100 km/h on many Canadian highways, and anywhere from 55 to 80 mph on US interstates depending on the state. Always follow the signs.
Tip: Canadian and many rental-car speedometers show both scales. The inner ring is usually the secondary unit.
Running race distances
| Race | Kilometers | Miles |
|---|---|---|
| 5K | 5 km | 3.11 mi |
| 10K | 10 km | 6.21 mi |
| 10 miles | 16.09 km | 10 mi |
| Half marathon | 21.0975 km | 13.11 mi |
| Marathon | 42.195 km | 26.22 mi |
To convert a running pace, divide: a pace of 5 minutes per km is 5 × 1.609344 = 8.05 minutes per mile, or about 8:03 per mile.
Common mistakes
- Using 1.6 for long distances. It is close, but on 500 miles 1.6 gives 800 km instead of 804.7 km.
- Confusing nautical and statute miles. A knot is one nautical mile (1.852 km) per hour, not one ordinary mile per hour.
- Converting pace like speed. Pace (minutes per km) converts the opposite way to speed: multiply by 1.609 to get minutes per mile.
Convert any distance or speed
Use our length converter for kilometers, miles, nautical miles, yards and feet, and the speed converter for km/h, mph, meters per second and knots.
Frequently asked questions
Is a kilometer longer than a mile? No. A mile is about 1.6 times longer than a kilometer.
How many miles is 100 km? 100 × 0.621371 = 62.14 miles.
Why does the UK use miles but measure races in kilometers? UK road signs kept imperial units by law, while athletics adopted metric distances internationally, so British runners use both.
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