Speed Converter

Speed converter: mph, km/h, m/s, knots, and Mach

This converter relates six speed units used on roads, tracks, water, and in the air: meters per second, kilometers per hour, miles per hour, feet per second, knots, and Mach. Speed is distance over time, so every value translates exactly into the others (with Mach depending on air conditions). Below are the factors and the contexts where each unit rules.

The core conversion factors

• 1 m/s = 3.6 km/h = 2.23694 mph = 3.28084 ft/s
• 1 km/h = 0.277778 m/s = 0.621371 mph
• 1 mph = 1.60934 km/h = 0.44704 m/s
• 1 knot = 1.852 km/h = 1.15078 mph = 0.514444 m/s
• Mach 1 ≈ 343 m/s ≈ 1,235 km/h (dry air, 20°C, sea level)

Road speeds: mph and km/h

The everyday swap is mph to km/h and back. The US, UK, and a handful of others post limits in mph; most of the world uses km/h. A handy mental approximation: multiply mph by 1.6 (or add 60%) to get km/h. So a 70 mph motorway limit is roughly 112 km/h, and a 100 km/h limit is about 62 mph.

Science and sport: meters per second

Physics uses m/s because it is the SI unit. To convert m/s to km/h you simply multiply by 3.6 — one of the cleanest conversions there is. Sprinters are often timed this way: a 100 m dash in 10 seconds averages 10 m/s, which is 36 km/h or 22.4 mph.

Navigation: knots and Mach

Aviation and shipping report speed in knots — nautical miles per hour — because the nautical mile ties directly to latitude. One knot is 1.852 km/h. For high-speed flight, Mach expresses speed as a fraction of the local speed of sound. Since that speed falls with temperature, the same Mach number corresponds to a lower true airspeed at altitude than at sea level, which is why this converter notes its 343 m/s reference.

Related converters

• Length Converter — convert the distance part of a speed or pace.
• Time Converter — turn travel time between seconds, minutes, and hours.
• Temperature Converter — air temperature sets the speed of sound behind Mach.