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Speed converter

Convert between kilometres per hour, miles per hour, metres per second, knots and feet per second, with the running pace per kilometre and per mile worked out too.

The speed you have

The pace below the answer is the same speed as minutes per kilometre and per mile, which is how running and rowing are usually discussed.

Converted

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Enter a speed and pick the two units.

Four units, three of them exact

Speed units are distance divided by time, so they inherit their precision from the distance. Since 1959 the mile has been exactly 1,609.344 metres, which makes a mile per hour exactly 0.44704 m/s. A knot is exactly one nautical mile an hour, and a nautical mile is exactly 1,852 metres, so a knot is exactly 1.852 km/h.

The one that surprises people is the nautical mile. It is not a rounded version of a land mile, it is a different idea: one minute of latitude, which is why it makes chart navigation straightforward and why it survived while almost every other sea unit did not.

Pace is speed turned upside down

A cyclist says 30 km/h. A runner says a 5:00 kilometre. They are describing the same sort of thing in opposite directions: speed is distance over time, and pace is time over distance.

That reversal is why pace cannot be another entry in the unit list. Everything else on this page scales the same way, so a bigger number always means faster. With pace a bigger number means slower, and doubling your speed halves your pace. The tool works it out separately for that reason.

Some paces worth recognising:

  • 10 km/h is a 6:00 kilometre, or a 9:39 mile
  • 12 km/h is a 5:00 kilometre, or an 8:03 mile
  • 15 km/h is a 4:00 kilometre, or a 6:26 mile

Converting in your head

km/h to mph: take away a third, then add a little back. 100 minus a third is 67, and the true answer is 62. Closer still: five miles is eight kilometres, so multiply by five and divide by eight.

m/s to km/h: multiply by 3.6, which is exact. 10 m/s is 36 km/h. This is the one worth memorising, because metres per second is what physics and engineering work in while road signs are in kilometres per hour.

knots to km/h: add 85%, roughly. A little under double. 20 knots is 37 km/h.

What this does not do

It converts a number from one unit to another, and that is all. It knows nothing about wind, gradient, traffic or acceleration, so the figure you get out means exactly what the figure you put in meant.

In particular, an average speed over a journey is not the average of the speeds along it. Driving 60 km at 60 km/h and then 60 km at 30 km/h averages 40 km/h rather than 45, because more of the time was spent going slowly. Work out the average from the total distance and the total time rather than from the speeds.

Questions

How do I convert km/h to mph?
Divide by 1.609344, or multiply by 0.621371. So 100 km/h is 62.14 mph and 50 km/h is 31.07 mph. The rough version worth carrying is that five miles is about eight kilometres, which makes 80 km/h roughly 50 mph and is accurate to within half a percent.
What is a knot?
One nautical mile an hour, and a nautical mile is exactly 1,852 metres. So a knot is 1.852 km/h or about 1.15 mph. It is used at sea and in the air because a nautical mile is one minute of latitude, which makes navigation by chart far simpler. Saying 'knots per hour' is a mistake: the hour is already in the unit.
How do I turn a speed into a running pace?
Divide the distance by the speed. At 12 km/h you cover a kilometre in 1000 ÷ 3.33 metres per second, which is 300 seconds, a 5:00 kilometre. This tool works out both the per kilometre and the per mile pace for whatever speed you enter, so you do not have to.
Why does a faster speed give a smaller pace?
Because they are reciprocals rather than different units of the same thing. Speed is distance over time and pace is time over distance, so doubling your speed halves your pace. That is why a converter cannot simply list pace among the units: it runs the other way.
How fast is 1 m/s?
3.6 km/h, or about 2.24 mph, which is a slow walk. Metres per second is the physics unit and the one most calculations are done in, which is why it is worth being able to place it: 10 m/s is 36 km/h, and the fastest humans reach roughly 12 m/s over a short sprint.
Is a mile per hour an exact figure?
Yes. A mile is exactly 1,609.344 metres by the 1959 international agreement, and an hour is exactly 3,600 seconds, so a mile per hour is exactly 0.44704 metres per second. Every digit this tool prints from that is real rather than rounded.
Does this account for wind, hills or traffic?
No. This converts a speed from one unit to another, and nothing else. It is an average figure in whatever unit you give it, so if the speed you enter already allows for conditions then so does the answer, and if it does not then the answer does not either.
Does anything I type here get sent anywhere?
No. The conversion runs in your browser, in the page you are already looking at. Nothing is uploaded, stored or logged, and closing the tab clears it. You can disconnect from the internet and the tool will keep working.

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