Speed Converter (m/s, km/h, mph, knots)
Convert speed between metres per second, kilometres per hour, miles per hour, feet per second, and knots — one value into every unit, with a reference table.
Speed conversion reference
| 1 unit | m/s | km/h | mph | kn |
|---|---|---|---|---|
| 1 m/s | 1 | 3.6 | 2.23694 | 1.94385 |
| 1 km/h | 0.277778 | 1 | 0.621371 | 0.539957 |
| 1 mph | 0.44704 | 1.60934 | 1 | 0.868977 |
| 1 ft/s | 0.3048 | 1.09728 | 0.681818 | 0.592484 |
| 1 kn | 0.514444 | 1.852 | 1.15078 | 1 |
Converting speed units
Speed is distance over time, so its units pair a length unit with a time unit — metres per second in science, kilometres per hour and miles per hour on the road, and knots (nautical miles per hour) at sea and in the air. This tool converts one value into all of them at once, working through metres per second internally.
Handy conversions to remember
The everyday one is m/s to km/h: multiply by 3.6 (there are 3600 seconds in an hour and 1000 metres in a kilometre). Miles and kilometres relate by the same 1.609 factor as any distance, so 1 mph ≈ 1.609 km/h and, roughly, a motorway 100 km/h ≈ 62 mph. A knot is 1.852 km/h — a nautical mile is slightly longer than a statute mile.
Worked example
A 100 km/h speed limit is 100 / 3.6 ≈ 27.78 m/s, or 100 / 1.609 ≈ 62.14 mph. A 10-second-per-100 m sprinter averages 10 m/s, which is 36 km/h — briefly faster than urban traffic.
Related
Convert the distance on its own with thelength converter.
Common questions
- How many mph is 100 km/h?
- About 62.14 mph. The conversion factor is exact by definition — a mile is 1.609344 km — so 100 / 1.609344 = 62.137. The rough mental version is to multiply km/h by 0.6 and add a little, which gets you to 60 and is close enough for reading a speed limit sign.
- What exactly is a knot?
- One nautical mile per hour, where a nautical mile is exactly 1,852 metres — so a knot is 1.852 km/h precisely. The definition is geographic rather than arbitrary: a nautical mile is close to one minute of latitude, which means a navigator can read distance straight off a chart's latitude scale. That is why marine and aviation speeds are still quoted this way.
- Why isn't converting km/h to mph just multiplying by 0.6?
- Because the true factor is 0.6214, so the shortcut runs about 3.5% low — fine for a rough sense, misleading for anything measured. On a 130 km/h motorway limit the shortcut says 78 mph when the real figure is 80.8. Use it as a sanity check, not as the conversion.
- What speed is Mach 1?
- It depends on the air, which is why Mach is a ratio rather than a fixed speed. The speed of sound varies with temperature — roughly 1,225 km/h at sea level on a standard day, but only about 1,062 km/h in the thin cold air at cruising altitude. So an aircraft at Mach 0.85 is travelling at very different ground speeds depending on where it is flying.