Speed Converter

Kilometers per hour (km/h) and miles per hour (mph) are both units of speed. 1 km/h = 0.6214 mph, and 1 mph = 1.6093 km/h. Most countries use km/h, while the US, UK (partially), and a few others use mph.

Mach number is the ratio of speed to the speed of sound. Mach 1 = speed of sound (~343 m/s or ~1,235 km/h at sea level, 20 C). Fighter jets can reach Mach 2-3. The Concorde flew at Mach 2.04.

A knot is a unit of speed equal to one nautical mile per hour (1.852 km/h or 1.151 mph). It is used in maritime and aviation. 1 knot is approximately 0.5144 m/s.

The speed of light in vacuum is exactly 299,792,458 meters per second (~300,000 km/s). It is the universal speed limit. Light from the Sun takes about 8 minutes 20 seconds to reach Earth.

The speed of sound varies by medium and temperature. In dry air at 20 C, it is approximately 343 m/s (1,235 km/h or 767 mph). In water, sound travels about 4.3x faster.

The fastest human-made object is the Parker Solar Probe, reaching ~692,000 km/h. For crewed flight, Apollo 10 holds the record at 39,897 km/h. Usain Bolt top running speed was 44.72 km/h.