How do you convert m/s to km/h?
Type a speed in metres per second and the answer appears in kilometres per hour as you type. The factor is 3.6 exactly, because there are 3600 seconds in an hour and 1000 metres in a kilometre, and 3600 divided by 1000 is 3.6.
It's the easiest conversion on this site to do in your head. Multiply by 3.6 going one way, divide by 3.6 coming back.
Why is m/s the proper unit?
Metres per second is the SI unit of speed, and it's the one every equation in physics is written in. That's not just convention. It's what makes the equations work without correction factors.
Acceleration is metres per second squared. Force is kilogram-metres per second squared. Kinetic energy is ½mv², which only comes out in joules if v is in metres per second. Put km/h into any of those and you have to carry a conversion factor through the whole calculation, and sooner or later you'll drop it.
Where do you meet it?
- Physics and engineering, everywhere. Every SI formula assumes it.
- Weather forecasts in most of the world. Wind in m/s is standard outside the English-speaking countries and aviation.
- Athletics, for wind readings. A sprint or long jump record is void if the following wind is over +2.0 m/s.
- Lifts and escalators, which are specified in m/s. A fast office lift does 6 m/s. An escalator does 0.5.
- Impact testing, where energy calculations dominate.
Speeds in metres per second
| Thing | m/s | km/h |
|---|---|---|
| Walking | 1.4 | 5.0 |
| Running | 3.3 | 12.0 |
| Cycling | 7.0 | 25.2 |
| Usain Bolt at peak | 12.4 | 44.6 |
| Urban speed limit | 13.9 | 50 |
| Motorway | 36.1 | 130 |
| Cheetah sprinting | 29 | 104 |
| Terminal velocity | 55 | 198 |
| Speed of sound at sea level | 343 | 1235 |
| Low Earth orbit | 7800 | 28,080 |
A worked example
A car doing 90 km/h brakes to a stop in 4 seconds. What's the deceleration?
Convert first: 90 divided by 3.6 is 25 m/s. Then a = Δv / t = 25 / 4 = 6.25 m/s², which is about 0.64g. Firm braking, but well within what a road tyre can do.
Try that in km/h and hours and you get an answer in kilometres per hour squared, a unit nobody has ever wanted. That's the whole reason the SI unit exists.
Wind and the athletics limit
World Athletics won't ratify sprint or horizontal-jump records set with a following wind over +2.0 m/s. That's 7.2 km/h, a gentle breeze that barely moves leaves, and enough to be worth a measurable fraction of a second over 100 m. It's the single most consequential m/s figure most people ever run into.
Frequently asked questions
How do I convert m/s to km/h?
Multiply by 3.6. So 25 m/s is 90 km/h. Divide by 3.6 to go the other way.
Why is the factor exactly 3.6?
3600 seconds in an hour, 1000 metres in a kilometre. 3600 divided by 1000 is 3.6, with no rounding anywhere.
What is 10 m/s in km/h?
36 km/h, or 22.4 mph. The anchor worth memorising.
Why does physics use m/s rather than km/h?
Because it's the SI unit and every derived unit is built on it. Acceleration, force and kinetic energy only come out right when speed is in metres per second.
What wind speed invalidates a sprint record?
A following wind above +2.0 m/s, which is 7.2 km/h. Records set above that aren't ratified.