Speed Converter
Enter a speed, choose your units, and watch the result update as you type. The table below shows the same speed in every unit at once — nothing you enter ever leaves your browser.
Enter a number to see the conversion.
| Kilometers per hour (km/h) | — |
|---|---|
| Miles per hour (mph) | — |
| Meters per second (m/s) | — |
| Knots (kn) | — |
Four speed units, one exact set of conversion factors
Every conversion here runs through meters per second as a common base, using conversion factors that are exact definitions rather than rounded approximations. 1 kilometer per hour is exactly 1⁄3.6 m/s, from the plain definitions of the kilometer and the hour. 1 mile per hour is exactly 0.44704 m/s, fixed by the 1959 international agreement that set the yard at exactly 0.9144 meters. 1 knot — one nautical mile per hour — is exactly 0.514444 m/s, since the international nautical mile is defined as 1,852 meters. Because every factor is exact, the only limit on precision here is floating-point arithmetic, not the constants themselves.
Worked example
Convert 100 km/h and you get about 62.137 mph, 27.778 m/s, and 53.996 knots — all four appear in the reference table the moment you type. Switch the "From" unit to knots instead and enter 100, and the result becomes about 185.2 km/h, since a knot covers more ground per hour than a kilometer does.
Frequently asked questions
Why isn't 1 km/h exactly 0.3 m/s?
It's close, but the exact value is 1⁄3.6 m/s ≈ 0.277778 m/s. That comes straight from the definitions: a kilometer is 1,000 meters and an hour is 3,600 seconds, so 1 km/h = 1,000 m ÷ 3,600 s = 1⁄3.6 m/s. This converter uses that exact fraction internally rather than a rounded decimal, so chained conversions don't drift.
What's the difference between a knot and mph?
Both measure distance per hour, but a different distance. A knot is one nautical mile (1,852 m) per hour, the unit used worldwide in aviation and at sea regardless of country. Mph is one statute mile (1,609.344 m) per hour, the everyday US road unit. Because a nautical mile is longer, a knot is a bit faster than a mph: 1 knot ≈ 1.15078 mph.
How precise are these conversions?
All three non-metric factors are exact defined constants, not measurements: 1 km/h = 1⁄3.6 m/s exactly, 1 mph = 0.44704 m/s exactly (from the 1959 international agreement fixing the yard at exactly 0.9144 m), and 1 knot = 0.514444 m/s (1,852 m per 3,600 s, from the international nautical mile). Because every factor is exact, the only limit on precision here is floating-point arithmetic — never the constants themselves.
Why do different countries and industries use different speed units?
Road signs and weather reports follow whatever unit system a country adopted for everyday measurement — mph in the US, km/h almost everywhere else. Aviation and maritime navigation are the exception: both use knots worldwide, regardless of a pilot's or ship's home country, because charts and airspace separation standards are set internationally.