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Convert mph to km/h
1 mph = 1.609344 km/h
Type a value in miles per hour and the answer in kilometres per hour appears as you go. The conversion is exactly 1.609344 km/h to the mile per hour, and it happens on your own machine — this page asks nothing of a server once it has loaded.
Where it runs
In your browser. The number you type is never part of a request.
Exact by definition
1 mph is exactly 1.609344 km/h — a definition, not a rounded factor.
Answers as you type
No button, no wait. The worked answer is already on the page before any script runs.
Mile per hour and Kilometre per hour
Miles per hour is the road speed of the United States and the United Kingdom, which is a rare pairing — the UK uses miles for road speed and metric for nearly everything else.
Kilometres per hour is the speed limit almost everywhere in the world. Dividing by 3.6 gives metres per second, because there are 3,600 seconds in an hour and 1,000 metres in a kilometre.
miles per hour to kilometres per hour in practice
70 mph is 112.7 km/h
— the British motorway limit.
30 mph is 48.28 km/h
— a British urban speed limit.
miles per hour to kilometres per hour at a glance
| mph | km/h |
|---|---|
| 1 | 1.609344 |
| 2 | 3.218688 |
| 3 | 4.828032 |
| 5 | 8.04672 |
| 10 | 16.09344 |
| 20 | 32.18688 |
| 50 | 80.4672 |
| 100 | 160.9344 |
Every figure here is computed from the same definition the calculator uses, so the table cannot drift away from the answer above it.
Convert mph to km/h: common questions
How many kilometres per hour are in a mile per hour?
Exactly 1.609344. One mile per hour is 1.609344 kilometres per hour, and the box above will do it for any figure you type.
Is this conversion exact, or rounded?
The ratio is exact. It is not a rounded constant typed into a table: it is derived from the definitions of the two units, so it agrees with any other correct converter to as many digits as you care to compare.
Why does another converter show a slightly different number?
Almost always rounding rather than disagreement. Many converters cut the answer to two or four decimals, and some carry a factor that was rounded before the multiplication rather than after. The figures here are computed from the exact definitions and only rounded on the way to the screen.
Where these figures come from
The claims this page makes about speed units are checkable, and these are the documents that settle them.
How this page works
The factor is a constant in the page and the arithmetic is four operations, so nothing is sent anywhere and nothing needs to be. The number you type never leaves the browser — there is no request for it to travel in.