Speed Converter

It routes every conversion through meters per second as one common base unit. Your value is multiplied by the From unit's meters-per-second factor, then that amount is divided by the To unit's own factor. Because speed is distance divided by time, each factor is built from an exact distance over an exact time: 1 km/h is 1000 m over 3600 s, 1 mph is 1609.344 m over 3600 s (exactly 0.44704 m/s), 1 ft/s is 0.3048 m over 1 s, and 1 knot is 1852 m over 3600 s.

Multiply the km/h value by about 0.6214 (this is 1000 divided by 1,609.344, the number of metres in a statute mile). So 100 km/h is roughly 62.14 mph. To go the other way, multiply mph by exactly 1.609344 to get km/h.

A knot is one nautical mile per hour, used for the speed of ships and aircraft. One international nautical mile is exactly 1,852 metres (adopted internationally in 1929 and by the United States in 1954), so 1 knot is exactly 1.852 km/h, about 1.1508 mph, and about 0.5144 m/s.

They use different miles. A knot is based on the nautical mile (1,852 m), while miles per hour uses the statute mile (1,609.344 m). The nautical mile is about 15 percent longer, so 1 knot is about 1.1508 mph, not 1. This converter keeps the two distinct rather than treating a knot as roughly a mph.

Decimals are fine - enter any value such as 27.5 and it converts normally. Results are shown to 4 decimal places by default; a very small result that would otherwise round to 0 is shown with extra decimal places instead, so a genuinely nonzero result is never displayed as zero. Negative values are rejected, since this converts a speed (a magnitude), not a signed velocity; zero is accepted.