Speed Converter

A speed converter turns kilometres per hour into miles per hour, metres per second and knots — 100 km/h is 62.14 mph, 1 metre per second is 3.6 km/h, and 1 knot is exactly 1.852 km/h. Speed is a compound unit, a distance divided by a time, which is why converting it means converting both parts: metres per second to kilometres per hour multiplies the distance by a thousandth and the time by 3,600, and the two combine into a single factor of 3.6. This page handles that for you, and runs entirely in your browser.

How to use it

1. Choose the unit you have and the unit you want.
2. Type the speed — the answer appears as you type.
3. Everything converts through metres per second, which is the physical base unit for speed.
4. Knots are included because aviation and shipping use them exclusively, and they are not interchangeable with miles per hour.

Examples

• 100 km/h = 62.1371 mph.
• 1 knot = 1.852 km/h, exactly.
• 1 metre per second = 3.6 km/h.
• A 100 m sprint in 10 seconds = 10 metres per second = 36 km/h.

Frequently asked questions

How many mph is 100 km/h?

62.1371 mph. The rough version is to take about five eighths, or multiply by 0.6 and add a little, which is accurate enough to read a foreign speed limit safely. The most useful pairs to memorise are the common limits: 50 km/h is 31 mph, 100 km/h is 62 mph, and 120 km/h is 75 mph. Going the other way, 30 mph is 48 km/h and 70 mph is 113 km/h.

What is a knot, and why do ships use it?

A knot is one nautical mile per hour, which is exactly 1.852 kilometres per hour. It survives at sea and in the air because it fits how navigation actually works: a nautical mile is one minute of latitude, so a ship travelling at 10 knots covers 10 minutes of latitude in an hour, and that can be read directly off a chart. The name comes from the old method of measuring it — a knotted rope paid out behind the ship, with the knots counted against a sandglass. Note that a knot already contains per hour, so knots per hour is a mistake.

How do I convert metres per second to km/h?

Multiply by 3.6. The factor comes from doing both halves of the unit at once: there are 3,600 seconds in an hour and 1,000 metres in a kilometre, and 3,600 divided by 1,000 is 3.6. So 10 metres per second is 36 km/h. Going the other way, divide by 3.6 — a 100 km/h motorway speed is about 27.8 metres per second, which is a useful figure for thinking about stopping distances, since it tells you how far the car travels during a one-second reaction.

How fast is the speed limit where I am driving?

Most of the world posts limits in kilometres per hour; the United States and the United Kingdom post them in miles per hour. The useful conversions are 30 mph = 48 km/h, 50 km/h = 31 mph, 70 mph = 113 km/h and 120 km/h = 75 mph. A hired car will usually show both on the dial, with one set of numbers smaller — check which ring you are reading before trusting it, because misreading a 120 km/h dial as mph is a very expensive mistake.

How do running paces relate to speed?

They are the same information inverted. Speed is distance over time and pace is time over distance, so a runner moving at 12 km/h is running 5 minutes per kilometre, and one at 10 km/h is running 6 minutes per kilometre. Divide 60 by the speed in km/h to get minutes per kilometre. Runners generally think in pace because it maps onto how a race is planned, while this converter works in speed — convert here first if a training plan gives you one and you want the other.