Speed Converter

A mile per hour uses the land mile, 1609.344 m, which makes it 0.44704 m/s. A knot uses the nautical mile, 1852 m, which makes it 0.514444 m/s — about 1.852 km/h. Both km/h and knots are repeating decimals, so the only rounding you see is the display.

Five units, twenty directed pairs, one pivot: metres per second. Each unit holds a single number, its worth in m/s, and a conversion multiplies by the factor of the unit you have and divides by the factor of the unit you want. Keeping five factors instead of twenty stored rates means the km/h-to-mph answer and the mph-to-km/h answer cannot contradict each other, and a new unit would cost one line rather than a new row and column. Speed factors are built from two exact definitions, a length and an hour of 3600 seconds. A mile is exactly 1609.344 m, so a mile per hour is exactly 0.44704 m/s; a foot is exactly 0.3048 m, so a foot per second is 0.3048 m/s. Kilometres per hour and knots come out as repeating decimals — 1000 ÷ 3600 and 1852 ÷ 3600 — but repeating is not the same as rounded. The ratio is exact; only the six decimals on screen are not, which is why 100 km/h shows as 62.137119224 mph. The distinction to hold on to is which mile is meant. Miles per hour uses the land mile of 1609.344 m, while a knot is one nautical mile per hour, 1852 m — so a knot is 1.852 km/h, or 1.150779 mph, about 15 % more. Twenty knots of wind is 37.04 km/h; twenty mph would be 32.18688 km/h.