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

What this converter does

If you grew up reading speeds in miles per hour and you are suddenly looking at a road sign, a car spec, or a weather report in kilometres per hour, this converter closes the gap. Type a speed in mph and it gives you the same speed in km/h. It is the conversion most people reach for when they drive somewhere that uses the metric system, since almost every country outside the US and a handful of others marks its limits in km/h.

The exact relationship

One mile is 1.60934 kilometres, so one mile per hour is 1.60934 kilometres per hour. To go from mph to km/h, you multiply:

km/h = mph × 1.60934

That number comes straight from the definition of a mile, so it does not change. Every mph figure is simply scaled up by about 61 percent to land in km/h, which is why km/h numbers always look bigger than the mph ones they came from.

Doing it in your head

For a quick estimate, multiply by 1.6. An easy way to hold that is the eight-fifths trick: divide by five, then multiply by eight. Take 30 mph, divide by five to get 6, times eight is 48, and the exact answer is 48.28 km/h, so you are spot on. If mental fifths are not your thing, just take the mph and add a bit more than half of it again. Either way you will be within a fraction of the real figure, which is plenty for reading a speed limit at a glance.

A worked example

Say your speedometer reads 65 mph on a US highway, and you want to know what that is where the signs are metric.

• 65 × 1.60934 = 104.6 km/h

So 65 mph is about 104.6 km/h. If the metric limit on a similar road is 100 km/h, that tells you straight away you would be a touch over it, which is exactly the kind of thing worth knowing before you settle into a cruise.

Common mph speeds in km/h

A few of these are worth remembering as anchors. A 30 mph town limit is about 48 km/h, the common 60 mph is roughly 96.6 km/h, and 70 mph sits just over 112 km/h.

Where you will use it

The everyday case is driving abroad, where you are reading your own mph speedometer against limits posted in km/h, or driving a hire car whose dial is marked the metric way. Beyond that, it comes up when you read a car's performance figures across regions, since a top speed quoted in one unit means little until you put it in the one you think in. Cyclists and runners hit it too, comparing a pace given in mph against training plans or race information written in km/h. Anywhere a speed crosses from the imperial world into the metric one, this is the conversion that makes it readable.

Questions people ask

How do I convert mph to km/h?

Multiply the speed in mph by 1.60934. For a rough figure in your head, multiply by 1.6, or divide by five and multiply by eight.

What is 60 mph in km/h?

About 96.56 km/h. That is a useful one to remember, since 60 mph is a common highway speed.

Why is the km/h number always bigger?

Because a kilometre is shorter than a mile, it takes more of them to cover the same distance in an hour. So the same speed is a larger number in km/h than 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