Kilometers per Hour to Miles per Hour Converter | km/h to mph

What this converter does

Most of the world measures speed in kilometres per hour, so if you are heading somewhere that still uses miles per hour, or reading a figure written for an American or British audience, you need it the other way round. This converter takes a speed in km/h and gives you the mph equivalent. Enter the number and you have it.

The exact relationship

Since a kilometre is 0.621371 of a mile, a kilometre per hour is 0.621371 of a mile per hour. Going from km/h to mph means multiplying:

mph = km/h × 0.621371

This is just the mph-to-km/h relationship flipped over, so the mph figure always comes out smaller than the km/h one you started with, by a little under 40 percent.

A quick mental shortcut

For a fast guess, multiply by 0.6, or take off about 40 percent. If you like neat fractions, five-eighths works nicely: halve the number, then add one-eighth of the original. Take 100 km/h, half is 50, one-eighth is 12.5, add them for 62.5, and the real answer is 62.1 mph. For most road speeds, this lands very close.

A worked example

Say you are on a French autoroute where the limit is 130 km/h, and you want that in the mph your instincts are tuned to.

• 130 × 0.621371 = 80.8 mph

So 130 km/h is about 80.8 mph. That is a handy figure to carry, because it tells you the fastest motorway limit in much of Europe sits around 80 mph, a fair bit above the 70 mph many drivers from the UK are used to.

Common km/h speeds in mph

Worth keeping in mind: a 50 km/h town limit is about 31 mph, 100 km/h is almost exactly 62 mph, and 120 km/h works out near 75 mph.

When this comes up

The classic case is a driver from a metric country visiting the US or UK, reading limits in mph while thinking in km/h. It also turns up the moment you read a car's figures the other way: a 0 to 100 km/h sprint time means one thing to a metric reader, but the same car's top speed is often quoted in mph in American reviews, and you want them in one language. Sports and athletics throw it up too, where a serve speed or a sprint might be reported in mph and you would rather see km/h, or the reverse. Whenever a metric speed needs to make sense to someone who counts in miles, this is the step.

Questions people ask

How do I convert km/h to mph?

Multiply the speed in km/h by 0.621371. In your head, multiply by 0.6 or take off roughly 40 percent for a quick estimate.

What is 100 km/h in mph?

About 62.14 mph. It is an easy anchor to remember, since 100 km/h is a common highway speed in metric countries.

Why is the mph number smaller?

A mile is longer than a kilometre, so you cover fewer miles than kilometres in the same hour. That makes the same speed a smaller number in mph.

References

1. National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (unit conversion factors). https://www.nist.gov/pml/special-publication-811