How do you convert mph to km/h?
Type a speed in miles per hour and the answer appears in kilometres per hour as you type. The factor is exact: one mph is 1.609344 km/h, because the international mile has been exactly 1609.344 metres since 1959.
Can I do it in my head?
Multiplying by 1.609 is awkward. Two shortcuts are close enough for the road:
- Add half, then a tenth of the original. 60 mph becomes 60 + 30 + 6 = 96 km/h. The real figure is 96.6, so that's accurate to well under 1%.
- Times 8, divide by 5. 70 mph goes to 560, then 112 km/h against a real 112.7. Easy to do in two steps.
- Or memorise the road anchors: 30 mph is about 48 km/h, 50 is about 80, and 70 is about 113.
UK and US limits in metric
| Limit | mph | km/h | Where |
|---|---|---|---|
| Built-up area | 20 | 32.2 | UK 20 mph zones |
| Urban | 30 | 48.3 | UK default built-up |
| US residential | 25 | 40.2 | Most US cities |
| Single carriageway | 60 | 96.6 | UK national limit |
| US highway | 55 | 88.5 | Older interstate limit |
| US interstate | 65 to 75 | 105 to 121 | Varies by state |
| Dual carriageway | 70 | 112.7 | UK |
| Texas SH-130 | 85 | 136.8 | Highest posted US limit |
Why 70 mph, and why 113 looks odd
The UK motorway limit of 70 mph was set in 1965 and hasn't moved. Converted, it's 112.65 km/h, which is an ugly number. That's the point. Limits are round in the unit they were written in and awkward in the other. It works the same in reverse. France's 130 km/h is 80.8 mph, which no English-speaking country would ever have chosen to post.
Driving a metric car in the UK or US
- Most digital clusters can switch units in the vehicle settings menu. Do it before you set off, not at a junction.
- Analogue dials usually carry both, with mph in a smaller inner ring, or the other way round depending on the market.
- Hire cars are marked for the country they're hired in, which is worth checking before you cross a border.
- Or use the GPS speedometer here, which shows either unit on any vehicle because it takes nothing from the car.
Beyond the road
A few figures that come up often enough to be worth having. Marathon world record pace is about 12.9 mph (20.7 km/h). A fast tennis serve is 130 mph (209 km/h). Usain Bolt peaked at 27.8 mph (44.7 km/h). An airliner cruises at about 560 mph (900 km/h). For anything in knots, use the knots converter instead, because sea and air use a different mile again.
Frequently asked questions
How do I convert mph to km/h?
Multiply by 1.609344. So 60 mph is 96.56 km/h.
What is 70 mph in km/h?
112.65 km/h. That's the UK motorway limit, which is why European drivers see 113 on a British motorway.
What is 60 mph in km/h?
96.56 km/h. The UK national limit on a single carriageway.
Is there a quick way to estimate it?
Add half the number, then a tenth of the original. 60 becomes 60 + 30 + 6 = 96 km/h, against a real 96.6.
Why is a mile exactly 1609.344 metres?
The 1959 international yard and pound agreement set the yard at exactly 0.9144 metres. A mile is 1760 yards, so it's exactly 1609.344 metres. A definition, not a measurement.