How do you convert km/h to mph?
Type a speed in kilometres per hour and the answer appears in miles per hour as you type. Nothing to press, nothing sent anywhere, and it works with no connection once the page has loaded.
The exact factor is 0.621371. One km/h is 0.621371 mph, because a mile is defined as exactly 1609.344 metres.
Can I do it in my head?
Multiplying by 0.621371 at a junction isn't realistic. Two shortcuts get close enough:
- Halve it, add 10%. 100 km/h becomes 50 + 5 = 55 mph. The real answer is 62, so this runs about 11% low. Better as a lower bound than an estimate.
- Times 6, drop a zero, add a bit. 100 goes to 600, then 60, then add 2%. That lands on 61 or 62 and is accurate to about 1%.
- Or just remember three: 50 km/h is about 31 mph, 100 is about 62, and 130 is about 81. Nearly every road speed is close to one of them.
Speed limits you'll actually meet
| Limit | km/h | mph | Where |
|---|---|---|---|
| Residential | 30 | 18.6 | Most European cities |
| Urban | 50 | 31.1 | EU default |
| Urban (UK/US) | 48 | 30 | Built-up areas |
| Rural | 80 | 49.7 | France, Spain |
| Rural (UK) | 97 | 60 | Single carriageway |
| Interstate (US) | 105 | 65 | Typical |
| Motorway (UK) | 113 | 70 | Motorway |
| Motorway (EU) | 130 | 80.8 | France, Italy |
Why are there two units anyway?
Only three countries use mph on their road signs: the UK, the US and Liberia. Everywhere else runs on km/h.
It's historical. The metric system spread through most of the world over the nineteenth and twentieth centuries, but road signage is expensive and politically visible, so the last holdouts kept imperial on the roads even after science, industry and athletics had moved on. The UK is the clearest case. It buys petrol in litres, runs races over kilometres, and posts its speed limits in miles per hour.
Driving abroad
Hire cars in Europe are marked in km/h, sometimes with a small mph scale inside the dial and sometimes not at all. A digital cluster can usually be switched in the settings menu, which is worth doing before you leave the car park. If yours can't, the GPS speedometer on this site shows mph on any vehicle, because it takes nothing from the car.
Doing it exactly
To go from km/h to mph, divide by 1.609344, or multiply by 0.621371, which is the same thing. The other way, multiply by 1.609344. There's no rounding in the definition. The international mile has been exactly 1609.344 metres since 1959, so every figure in the table above is reproducible rather than conventional.
Frequently asked questions
How do I convert km/h to mph?
Multiply by 0.621371, or divide by 1.609344. So 100 km/h is 62.14 mph.
What is 100 km/h in mph?
62.14 mph. Worth memorising, since a lot of motorway driving happens near it.
What is 120 km/h in mph?
74.56 mph. A common limit across southern Europe.
Is there a quick way to estimate it?
Multiply by 6, drop a zero, add about 2%. So 130 goes to 780, then 78, then about 80 mph. The real figure is 80.8.
Which countries use mph?
The UK, the US and Liberia post road speed limits in miles per hour. Everywhere else uses km/h.