Speed converter: km/h and mph
Enter a speed in either unit. Useful for road signs, rental cars and speedometers.
One kilometer per hour equals 0.621371 mph, and one mph equals 1.609344 km/h. The factor is identical to converting distance.
The conversion
km/h = mph × 1.609344
Speed uses exactly the same factor as distance, because both units are just a distance divided by the same hour. If you can convert kilometers to miles, you can convert km/h to mph with the identical arithmetic.
Speed limits worth knowing
| km/h | mph | Typically |
|---|---|---|
| 30 | 19 | Urban, near schools |
| 50 | 31 | Built-up areas |
| 60 | 37 | Minor rural roads |
| 80 | 50 | Rural single carriageway |
| 90 | 56 | Rural roads, France |
| 100 | 62 | Expressway |
| 110 | 68 | Motorway, some countries |
| 120 | 75 | Motorway, much of Europe |
| 130 | 81 | Motorway, France and Italy |
The one that catches drivers out
A 30 mph limit is 48 km/h and a 50 km/h limit is 31 mph. They are close enough that a driver used to one system reads the other as roughly familiar and drives accordingly. On a 50 km/h street, driving at what feels like 30 leaves you at 48 km/h, which is fine. Reversed, on a 30 mph street, driving at 50 on a km/h speedometer puts you at 31 mph, which is over the limit.
The bigger trap is the motorway. 70 mph is 113 km/h, but 130 km/h is 81 mph. A driver moving between the UK and France who mentally swaps one for the other is out by 11 mph.
Doing it in your head
From km/h to mph, halve it and add a tenth of the original: 120 becomes 60 + 12 = 72, against a true 74.6. From mph to km/h, add half again plus a tenth: 70 becomes 70 + 35 + 7 = 112, against a true 112.7.
Metres per second
The calculator also shows m/s, which is the unit physics and engineering use. Divide km/h by 3.6 to get it. It is worth a glance because it makes stopping distances intuitive: at 100 km/h you are covering 27.8 metres every second, which is most of a reaction time before the brakes have done anything at all.
Next steps
Common questions
- How do I convert km/h to mph?
- Multiply by 0.621371. A 100 km/h limit is 62 mph, and a 120 km/h limit is 75 mph.
- What is 70 mph in km/h?
- 70 miles per hour is 112.65 km/h. This is the UK motorway limit, which is why it sits awkwardly between the 110 and 120 km/h limits used elsewhere in Europe.
- Is the speed conversion the same as the distance one?
- Yes. Both units are a distance divided by the same hour, so the factor is identical to converting kilometers to miles.
- What is 100 km/h in metres per second?
- 27.78 metres per second. Dividing km/h by 3.6 gives m/s, and it is a useful figure because it shows how much ground you cover during a reaction time.