Units of speed include: 1  metres per second (symbol m s−1 or m/s), the SI derived unit; 2  kilometres per hour (symbol km/h); 3  miles per hour (symbol mi/h or mph); 4  knots (nautical miles per hour, symbol kn or kt);  feet per second (symbol fps or ft/ 1 s); Mach number (dimensionless), speed divided by the speed of sound;