Kilometres per hour to miles per hour Converter

How many miles per hour are in a kilometre per hour?

One kilometre per hour is 0.621371 miles per hour. The full conversion is miles per hour = kilometres per hour × 0.6213711922, and going the other way you divide instead of multiply.

A few anchor values worth memorising: 0.621371 mph to the kilometre per hour, 6.213712 mph to ten, and 62.137119 mph to a hundred. The calculator above handles the rest, including the awkward decimals.

The reference table under the converter lists the values people look up most often, so for a common figure you can read the answer off directly rather than typing anything.

Worked examples

Three worked examples, each multiplying by 0.62137119:

2.5 km/h × 0.621371 = 1.5534 mph. 25 km/h × 0.621371 = 15.5343 mph. 250 km/h × 0.621371 = 155.3428 mph.

To reverse any of them, divide instead of multiplying — or use the swap button above, which does the same thing without the arithmetic. Reversing a converted value should return you to exactly what you started with; if it does not, something has been rounded too early.

Doing this conversion in your head

The exact factor is 0.62137119, which nobody multiplies by in their head. It is very close to 5/8, so multiplying by 5 and dividing by 8 lands within 0.58% of the correct answer — accurate enough for anything short of engineering work.

Since the factor is less than one, the number always gets smaller: a kilometre per hour is larger than a mile per hour, so any quantity converts to fewer of them. A result larger than what you started with means the conversion went the wrong way.

That sanity check catches the majority of real conversion errors. Before trusting any converted figure, ask whether the direction of change makes sense — it takes a second and it is the single most effective safeguard there is.

When you need to convert kilometres per hour to miles per hour

Most people arrive at this conversion from one of a few directions, each with its own tolerance for error.

On the source side, kilometres per hour is the speedometer and speed limit unit across most of the world. On the target side, miles per hour is the speed limit in the US and UK, and how wind speeds are reported in US forecasts. The conversion is essentially a translation between those two worlds — most often because a figure produced in one context has to be understood, submitted or acted on in the other.

Where the converted figure will be cut, dosed, billed or filed, round once at the end rather than at each step. For a rough sense of scale, round freely.

Whatever the reason, the arithmetic runs in your browser. Nothing you type is transmitted, logged or stored, and the converter keeps working if you go offline after the page has loaded.

What a kilometre per hour and a mile per hour actually are

The kilometre per hour (km/h). The road speed unit for most of the world.

The mile per hour (mph). Road speeds in the US and UK, and wind speeds in US weather reports.

Since kilometres per hour and miles per hour both quantify speed against a common defined standard, nothing is lost in translating between them. The only imprecision anywhere in this page is deliberate rounding for readability.

Common mistakes when converting kilometres per hour to miles per hour

Watch the direction. Because kilometre per hour and mile per hour are close enough in magnitude to look interchangeable at a glance, converting the wrong way is easy and rarely obvious from the result alone. Check that the number moved the way you expected before using it.

If you are converting many values, change the source unit in the dropdown rather than converting through an intermediate unit. Every extra hop is another rounding opportunity.