Speed Converter

Convert between km/h, mph, m/s, and knots, with how each speed unit is built from distance and time explained.

Speed Is Always Distance Divided by Time, Even When It Doesn’t Look Like It

Every speed unit is fundamentally a distance unit divided by a time unit, which is why converting between them always comes down to combining the underlying distance conversion with the underlying time conversion rather than needing any separate logic of its own. Kilometres per hour and miles per hour are the most familiar pairing, and converting between them is simply the kilometre-to-mile ratio applied directly, since the “per hour” part of both units is identical and cancels out. Metres per second, the SI unit favoured in physics and engineering, uses a much smaller distance unit over a much smaller time unit, which is why the numbers look so different at a glance, even though 27.8 metres per second and 100 kilometres per hour describe exactly the same speed. Knots stand apart from the others because they’re built on the nautical mile rather than the standard mile or kilometre, and the nautical mile itself was deliberately defined from Earth’s circumference, specifically as one minute of latitude, making a knot directly meaningful for navigation in a way that lines up cleanly with charts and coordinates, which is exactly why aviation and maritime navigation have continued using knots long after most everyday contexts moved to kilometres or miles per hour.