The formula
km/h = m/s × 3.6
Where the factor comes from — each unit by its definition, then its size in SI:
1 m/s is the SI unit of speed.1 km/h = km / h = 0.277777777778 m/s
Dividing the two SI sizes gives the factor: 3.6, exact — every step above is a definition, not a measurement. The reverse factor is 0.277777777778.
Kinematics and energy formulas need speed in metres per second. Road speeds come in km/h or mph, so convert before you square anything: kinetic energy goes with v², so a unit slip is squared too.
Worked examples
- Motorway driving: 27.7778 m/s = 100 km/h — 27.7778 × 3.6 = 100
- A brisk walk: 1.38889 m/s = 5 km/h — 1.38889 × 3.6 = 5
- US highway driving (60 mph): 26.8224 m/s = 96.5606 km/h — 26.8224 × 3.6 = 96.5606
- A hard-thrown ball: 30 m/s = 108 km/h — 30 × 3.6 = 108
Frequently asked questions
How many kilometres per hour is 1 m/s?
1 m/s = 3.6 km/h, exactly, from the unit definitions.
How do I convert kilometres per hour back to metres per second?
Divide by 3.6 — or multiply by 0.277777777778: 1 km/h = 0.277777777778 m/s.