m/s to km/h

Multiply by 3.6. To go back, divide by 3.6.

Where 3.6 comes from

There are 1,000 metres in a kilometre and 3,600 seconds in an hour. So:

1 m/s = 3,600 m/hour = 3.6 km/h

That is the whole derivation. The factor is exact, not rounded, which is why m/s and km/h convert so cleanly compared with anything involving miles.

Why science uses m/s

The metre per second is the SI derived unit for speed, and it is what every physics equation expects. Acceleration is m/s², force calculations assume m/s, and kinetic energy is ½mv² with v in m/s. Feed km/h into any of those and the answer is wrong by a factor of 12.96.

Road signs use km/h purely because the numbers are more convenient for humans: "50" reads better than "13.9".

Reference points

GPS reports speed in m/s

Worth knowing if you ever work with location data directly. The Web Geolocation API's coords.speed field is always in metres per second, regardless of what units the page displays.

Self Speed holds every internal calculation in m/s and converts only at the point of display, which avoids compounding rounding errors across unit switches. You can select m/s as a display unit directly if you prefer it.