mph, km/h, knots and m/s
All of these are exact multiples of each other, except Mach: 1 mile = 1,609.344 m and 1 nautical mile = 1,852 m by definition, so 1 mph = 1.609344 km/h and 1 knot = 1.852 km/h exactly.
- mph: road speeds in the US and UK.
- km/h: road speeds almost everywhere else. Divide by 3.6 to get m/s.
- Knots (kn): aviation, sailing and wind reports; 1 kn = 1 nautical mile per hour = 1.15078 mph.
- m/s and ft/s: physics, engineering and some wind forecasts.
- Mach: speed relative to the speed of sound, which depends on air temperature. This converter assumes sea level at 15 °C (International Standard Atmosphere): 340.29 m/s = 1,225.04 km/h. At airliner cruise altitude the speed of sound is only about 295 m/s.
1 mph = 1.609344 km/h (exact) 1 km/h = 0.621371 mph
1 kn = 1.852 km/h (exact) 1 kn = 1.15078 mph
1 m/s = 3.6 km/h Mach 1 = 340.29 m/s (15 °C, sea level)
mph to km/h table
| mph | km/h | m/s |
|---|---|---|
| 5 mph | 8.0467 | 2.2352 |
| 10 mph | 16.093 | 4.4704 |
| 15 mph | 24.14 | 6.7056 |
| 20 mph | 32.187 | 8.9408 |
| 25 mph | 40.234 | 11.176 |
| 30 mph | 48.28 | 13.411 |
| 35 mph | 56.327 | 15.646 |
| 40 mph | 64.374 | 17.882 |
| 45 mph | 72.42 | 20.117 |
| 50 mph | 80.467 | 22.352 |
| 55 mph | 88.514 | 24.587 |
| 60 mph | 96.561 | 26.822 |
| 65 mph | 104.61 | 29.058 |
| 70 mph | 112.65 | 31.293 |
| 75 mph | 120.7 | 33.528 |
| 80 mph | 128.75 | 35.763 |
| 100 mph | 160.93 | 44.704 |
Worked example
A 70 mph interstate limit is 70 × 1.609344 = 112.65 km/h. A 20-knot breeze is 23.02 mph (37.04 km/h).
Frequently asked questions
How many km/h is 1 mph?
1 mph = 1.609344 km/h exactly; 1 km/h = 0.621371 mph.
How fast is a knot?
1 knot = 1.852 km/h = 1.15078 mph, one nautical mile per hour.
How fast is Mach 1?
About 1,225 km/h (761 mph) at sea level and 15 °C; less at altitude, where the air is colder.