How to use the speed converter
Type a speed in the Value box, choose the unit you have and the unit you want, then press Convert. The swap button reverses the direction. A table under the result lists the same speed in all five supported units: meters per second, kilometers per hour, miles per hour, feet per second and knots.
It is useful for reading speed limits abroad, comparing running or cycling paces, wind speeds in weather reports, and boat or aircraft speeds.
How the conversion works
Every unit is a distance divided by a time, and the distances and times have exact definitions:
- 1 m/s = 3.6 km/h (3,600 seconds in an hour, 1,000 m in a km)
- 1 mph = 1,609.344 m per hour = 1.609344 km/h
- 1 ft/s = 0.3048 m/s
- 1 knot = 1 nautical mile per hour = 1,852 m per hour = 1.852 km/h
The converter goes through a common base of millimeters per hour, where all five units have whole-number factors, so these definitions are kept exactly.
Worked example
To convert a 100 km/h speed limit to mph: 100 / 1.609344 = 62.137119 mph (six decimals). Another handy check: 60 mph is exactly 88 feet per second, because 60 × 5,280 / 3,600 = 88.
Good to know
- For quick mental math, km/h × 0.62 is close to mph, and mph × 1.6 is close to km/h.
- Divide km/h by 3.6 to get m/s. For example, 36 km/h is exactly 10 m/s.
- A knot is about 15% faster than one mph, because a nautical mile is longer than a statute mile.
- Results show up to six decimals. Speeds here are magnitudes, so negative values are rejected; zero is allowed.