Quick answer: One mile per hour is exactly 1.609344 km/h, so 120 km/h = 74.564543 mph.
How it's calculated
The speed is changed to metres per second, then to your unit. 1 km/h = 1,000 m ÷ 3,600 s = 1/3.6 m/s; 1 mph = 1,609.344 m per hour = 0.44704 m/s; 1 knot = 1 nautical mile (1,852 m) per hour.
Quick rules: km/h ÷ 3.6 = m/s, km/h ÷ 1.609 = mph, and knots × 1.852 = km/h. For wind speeds and distance-time problems see the speed, distance and time calculator.
Worked examples
- Highway limit of 120 km/h: 120 km/h = 74.564543 mph
- Sprint of 10 m/s: 10 m/s = 36 km/h
- Ship at 20 knots: 20 kn = 37.04 km/h
Common speed conversions
| From | To |
|---|---|
| 1 m/s | 3.6 km/h |
| 1 km/h | 0.27777778 m/s |
| 1 mph | 1.609344 km/h |
| 1 kn | 1.852 km/h |
| 60 km/h | 37.282272 mph |
| 80 km/h | 49.709695 mph |
| 100 km/h | 62.137119 mph |
| 120 km/h | 74.564543 mph |
| 140 km/h | 86.991967 mph |
| 60 mph | 96.56064 km/h |
Frequently asked questions
How do I convert km/h to mph?
Divide by 1.609344. 100 km/h ≈ 62.14 mph.
How do I convert km/h to m/s?
Divide by 3.6. 36 km/h = 10 m/s.
What is a knot?
One nautical mile per hour, exactly 1.852 km/h. It is used for ships, aircraft and wind.
What is 120 km/h in mph?
About 74.6 mph. 120 km/h is a common motorway limit in the Gulf.
What is 100 mph in km/h?
About 161 km/h.
How fast is Mach 1?
It's the speed of sound, about 1,235 km/h at sea level on a mild day. Sound travels slower in cold air, so up where airliners cruise, Mach 1 is closer to 1,060 km/h.