The formula
mph = m/s × 2.236936292
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 mph = mi / h = 0.44704 m/s
Dividing the two SI sizes gives the factor: 2.23693629205 (rounded for display; the underlying ratio is fixed by the definitions). The reverse factor is 0.44704.
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 (100 km/h): 27.7778 m/s = 62.1371 mph — 27.7778 × 2.236936292 = 62.1371
- A brisk walk (5 km/h): 1.38889 m/s = 3.10686 mph — 1.38889 × 2.236936292 = 3.10686
- US highway driving: 26.8224 m/s = 60 mph — 26.8224 × 2.236936292 = 60
- A hard-thrown ball: 30 m/s = 67.1081 mph — 30 × 2.236936292 = 67.1081
Frequently asked questions
How many miles per hour is 1 m/s?
1 m/s = 2.23693629205 mph.
How do I convert miles per hour back to metres per second?
Divide by 2.23693629205 — or multiply by 0.44704: 1 mph = 0.44704 m/s.