Every unit here reduces to metres per second, using exact international definitions rather than rounded conversions — so a mile-per-hour figure converts to kilometres per hour without accumulating any rounding error along the way.
How it works
To metres per second
1 mph = 1609.344 ÷ 3600 = 0.44704 m/s exact
1 knot = 1852 ÷ 3600 = 0.514444… m/s exact
1 mile = 1609.344 m (the international mile, fixed in 1959). 1 nautical mile = 1852 m (fixed by international agreement in 1929). Both are used to derive every factor here, rather than each unit having its own separately-rounded constant.
Why a knot is not “a nautical mph”
It is exactly that, in fact — a knot is defined as one nautical mile per hour — but the nautical mile itself is a different length from the ordinary statute mile, about 15% longer. That difference is why a ship’s or aircraft’s speed in knots looks like a slightly smaller number than the same physical speed would show in mph, and it is a common source of confusion when comparing a boat’s speed to a car’s.
How to use this calculator
- Type a speed into any field.
- The others update immediately — km/h, mph and m/s up front, knots and feet per second behind “More units”.
Frequently asked questions
Why is a knot not the same as a mile per hour?
Because it is built on the nautical mile (1852 m), not the ordinary statute mile (1609.344 m). The two miles differ by about 15%, so 1 knot is about 1.15 mph, not exactly 1 mph.
Is 1609.344 m really the exact length of a mile?
Yes — the international mile was fixed at exactly 1609.344 metres by agreement among English-speaking countries in 1959, replacing several slightly different national definitions that existed before.
Why does aviation use knots instead of mph or km/h?
Because a knot relates directly to a nautical mile, and a nautical mile is defined to relate directly to a minute of latitude on the Earth’s surface — which makes navigation arithmetic against a map or chart considerably simpler than it would be in mph or km/h.
How accurate is the m/s conversion?
Exact for every unit shown, because every factor here is derived from the internationally fixed definitions of the mile, the nautical mile and the foot — none of them are rounded approximations.
