Speed Converter
Convert speed between kilometres per hour, miles per hour, metres per second, knots and Mach.
How it works
Speed is distance over time, so every unit here reduces to metres per second and converts by a single factor. The metric relationship worth memorising is that 1 m/s is exactly 3.6 km/h.
A knot is one nautical mile per hour, which makes it 1.852 km/h exactly. Aviation and shipping use it because a nautical mile is one minute of latitude, so speed in knots maps directly onto a chart.
Mach is not a fixed speed. It is a ratio against the local speed of sound, which falls with temperature and therefore with altitude — the figure here uses the standard sea-level value, so treat it as indicative rather than exact for a cruising aircraft.
The formula
km/h → mph
mph = km/h × 0.62137119
mph → km/h
km/h = mph ÷ 0.62137119
Any pair in this family
result = value × (factor of source ÷ factor of target)
Every unit is defined against the mps, so any combination converts in one step.
Worked examples
| Scenario | Working | Result |
|---|---|---|
| 100 km/h to mph | 100 × 0.621371 | 62.14 mph |
| 1 m/s to km/h | 1 × 3.6 | 3.6 km/h exactly |
| 10 knots to km/h | 10 × 1.852 | 18.52 km/h |
When you'd use it
- Reading a speed limit abroad
- Converting a running or cycling pace
- Working with marine or aviation speeds in knots
- Physics coursework needing m/s
Common questions
How do I convert m/s to km/h quickly?
Multiply by 3.6 — it is exact, since there are 3,600 seconds in an hour and 1,000 metres in a kilometre. Divide by 3.6 to go the other way.
Why do ships and aircraft use knots?
Because a knot is one nautical mile per hour, and a nautical mile is one minute of latitude. Speed in knots therefore converts directly into position on a chart, which is far more useful at sea than a land-based mile.
Is Mach 1 always the same speed?
No. Mach is a ratio to the local speed of sound, which depends on air temperature and so on altitude. Mach 1 is about 1,235 km/h at sea level but nearer 1,062 km/h in the cold air at cruising height. This tool uses the sea-level figure.
Is anything I enter sent anywhere?
No. Every conversion runs in your browser, so nothing you type is uploaded, logged or stored. There is no account and no record of what you converted.