The exact equivalent
One mile per hour is exactly 1.609344 kilometres per hour, the same factor as miles to kilometres.
1 mph = 1.609344 km/h
1 km/h = 0.62137119 mph
How to convert it by hand
Just multiply by the conversion factor. To go from miles per hour to kilometres per hour, multiply by 1.609344; to come back, divide by that same number or multiply by 0.621371.
For example: 25 mph × 1.609344 = 40.2336 km/h.
A tip that saves mistakes: check the result goes the way you expect. If kilometres per hour are a smaller unit than miles per hour, the number has to come out bigger. If it comes out smaller, you divided when you should have multiplied.
Conversion table
| mph | km/h |
|---|---|
| 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 |
|---|---|
| A UK motorway limit | 70 mph = 112.7 km/h |
| A US highway limit | 65 mph = 104.6 km/h |
| An urban limit | 30 mph = 48.3 km/h |
| A brisk walk | 3 mph = 4.8 km/h |
The trick for doing it in your head
Add 60%. For 70 mph: 70 plus 42 gives 112 km/h, against a true 112.7.
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.