# 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 ``` mph = km/h × 0.621371 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 Common limits in both units, rounded to the nearest whole number. | 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 - [convert the distance as well as the speed](https://www.kilometer-mileage.com/km-to-miles.html) - [work out what the journey costs in fuel](https://www.kilometer-mileage.com/fuel-cost-calculator.html) - [go the other way, miles into kilometers](https://www.kilometer-mileage.com/miles-to-km.html) ## Common questions