Speed Unit Reference
Kilometers per hour (km/h) is the standard for road speeds globally. Miles per hour (mph) is used in the US and UK. Meters per second (m/s) is the SI unit. Knots are used in aviation and maritime. Mach number represents multiples of the speed of sound (~343 m/s at sea level). The speed of light (c) is ~299,792,458 m/s.