About Speed Conversion
Speed measures how quickly an object covers distance. Its SI unit is the metre per second (m/s), but in everyday life we use units calibrated to our context: km/h on roads in most countries, mph on roads in the UK and US, knots for aviation and maritime navigation, and Mach for supersonic flight.
The tricky part of speed conversion is that each unit combines a length with a time. Converting between km/h and mph is not simply a ratio of kilometres to miles — it also involves hours staying equal. Since 1 hour equals 1 hour, the ratio is just the length ratio: 1 mph = 1.609344 km/h.
The 7 units supported
| Unit | Symbol | Metres per second |
|---|---|---|
| Metre per second | m/s | 1 |
| Kilometre per hour | km/h | 0.277778 (5/18 exactly) |
| Mile per hour | mph | 0.44704 exactly |
| Knot | kn | 0.514444… (1852/3600) |
| Foot per second | ft/s | 0.3048 exactly |
| Mach (sea level, 15 °C) | Ma | 340.29 |
| Speed of light | c | 299,792,458 exactly |
Common conversions
| From | To | Factor |
|---|---|---|
| 1 m/s | Kilometres per hour | 3.6 exactly |
| 1 km/h | Miles per hour | 0.621371… approximately |
| 1 mph | Kilometres per hour | 1.609344 exactly |
| 1 knot | Kilometres per hour | 1.852 exactly |
| 1 knot | Miles per hour | 1.150779… approximately |
| 1 mph | Feet per second | 1.466667… approximately |
Common reference speeds
| Activity | km/h | mph | m/s |
|---|---|---|---|
| Walking | 5 | 3.1 | 1.4 |
| Running | 12 | 7.5 | 3.3 |
| Cycling | 25 | 15.5 | 6.9 |
| City driving | 50 | 31.1 | 13.9 |
| Highway driving | 100 | 62.1 | 27.8 |
| High-speed train | 300 | 186.4 | 83.3 |
| Cruising airliner | 900 | 559.2 | 250 |
| Speed of sound (sea level) | 1,234.8 | 767.3 | 343 |
| Speed of light | 1.08 billion | 671 million | 299,792,458 |
Why Mach varies
The Mach number is a relative unit — Mach 1 is the speed of sound in the surrounding air, which depends on temperature. At sea level and 15 °C, the speed of sound is about 340.29 m/s. At 11 km altitude, where the temperature is around −56 °C, it drops to about 295 m/s. So Mach 2 at sea level and Mach 2 at cruise altitude correspond to different absolute speeds.
This tool uses the ISA (International Standard Atmosphere) sea level value of 340.29 m/s as the reference for Mach. If you need accurate supersonic calculations at altitude, use the appropriate local speed of sound rather than this approximation.
Common use cases
Driving Abroad
Convert speed limits and speedometer readings between km/h and mph.
Aviation
Convert knots to km/h or mph for flight planning.
Maritime
Convert knots to statute miles for shipping calculations.
Sports & Fitness
Convert running and cycling paces between units.
Science & Physics
Convert m/s for equations and Mach numbers for aerodynamics.
Weather & Wind
Convert wind speeds between knots, km/h and m/s.
Privacy and accuracy
This speed converter runs entirely in your browser. All conversions use exact definitional factors, so the results are as precise as the input. Nothing is uploaded, stored or logged.