The exact equivalent
A mile is exactly 1.609344 kilometres, which follows from the yard being defined as exactly 0.9144 metres.
1 mi = 1.609344 km
1 km = 0.62137119 mi
How to convert it by hand
Just multiply by the conversion factor. To go from miles to kilometres, multiply by 1.609344; to come back, divide by that same number or multiply by 0.621371.
For example: 25 mi × 1.609344 = 40.2336 km.
A tip that saves mistakes: check the result goes the way you expect. If kilometres are a smaller unit than miles, the number has to come out bigger. If it comes out smaller, you divided when you should have multiplied.
Conversion table
| mi | km |
|---|---|
| 1 | 1.6093 |
| 2 | 3.2187 |
| 5 | 8.0467 |
| 10 | 16.0934 |
| 20 | 32.1869 |
| 50 | 80.4672 |
| 100 | 160.9344 |
Reference points to picture it
| Reference | Equals |
|---|---|
| 1 mile | 1.61 km |
| A 26.2-mile marathon | 42.2 km |
| A 70 mph motorway limit | 112.7 km/h |
| New York to Boston | 215 miles = 346 km |
The trick for doing it in your head
Add 60%. For 50 miles: 50 plus 30 gives 80 km, against a true 80.5. Or run the Fibonacci trick backwards: 5 miles ≈ 8 km.
It is fine for getting by without a phone, but not for anything that depends on precision: in a recipe, on a building site or in a dose, use the exact conversion.