Speed Conversion Calculator
Speed Conversion Calculator
Speed is expressed in different units around the world and across contexts — km/h and m/s in most metric countries, mph on US and UK roads, knots in aviation and marine navigation, and Mach for supersonic aircraft.
This tool converts between all six directly, so you don't need to look up separate conversion factors for each pair.
- Key factors: 1 km/h = 0.277778 m/s; 1 mph = 0.44704 m/s exactly; 1 knot = 0.514444 m/s (1 nautical mile/hour).
- Mach is context-dependent: the speed of sound varies with air temperature and altitude — this converter uses the standard sea-level value (340.3 m/s at 15°C), a common reference point, not the exact local speed of sound at altitude.
- Fully flexible: change either dropdown to convert between any two of the six supported speed units.
How do I convert km/h to mph?
Multiply the km/h value by 0.621371, or select "Kilometers per hour" as From and "Miles per hour" as To in this converter.
Why does Mach depend on altitude?
The speed of sound decreases with lower air temperature, and temperature drops with altitude — so "Mach 1" at 35,000 feet is a slower absolute speed than "Mach 1" at sea level.
Speed Conversion Calculator
Speed is expressed in different units around the world and across contexts — km/h and m/s in most metric countries, mph on US and UK roads, knots in aviation and marine navigation, and Mach for supersonic aircraft.
This tool converts between all six directly, so you don't need to look up separate conversion factors for each pair.
- Key factors: 1 km/h = 0.277778 m/s; 1 mph = 0.44704 m/s exactly; 1 knot = 0.514444 m/s (1 nautical mile/hour).
- Mach is context-dependent: the speed of sound varies with air temperature and altitude — this converter uses the standard sea-level value (340.3 m/s at 15°C), a common reference point, not the exact local speed of sound at altitude.
- Fully flexible: change either dropdown to convert between any two of the six supported speed units.
How do I convert km/h to mph?
Multiply the km/h value by 0.621371, or select "Kilometers per hour" as From and "Miles per hour" as To in this converter.
Why does Mach depend on altitude?
The speed of sound decreases with lower air temperature, and temperature drops with altitude — so "Mach 1" at 35,000 feet is a slower absolute speed than "Mach 1" at sea level.