Speed Converter

1 kmph equals 0.6214 mph, and 1 mph equals 1.60934 kmph. So 100 kmph is about 62 mph and 60 mph is about 97 kmph. Indian and most international speedometers use kmph; US and UK speed limits use mph. For mental conversion, multiply kmph by 5 by 8 to get mph: 100 times 5 by 8 equals 62.5.

The speed of light in vacuum is 299,792,458 metres per second : about 3,00,000 km per second, or 1.08 billion kmph. Light takes 8.3 minutes to reach Earth from the Sun, and 1.3 seconds from the Moon. Nothing with mass can travel at light speed, per Einstein's theory of relativity.

Speed is how fast you are moving (a scalar, just a number with units). Velocity is speed in a specific direction (a vector). A car at 60 kmph north and a car at 60 kmph south have the same speed but opposite velocities. Day-to-day language usually says speed for both, but physics keeps them separate.

Multiply m/s by 3.6 to get kmph (because there are 3,600 seconds in an hour and 1,000 metres in a km). So 10 m/s equals 36 kmph, and 100 m/s equals 360 kmph. Going the other way, divide kmph by 3.6 to get m/s : a 90 kmph car is doing 25 m/s.

Mach 1 is the speed of sound, which is about 343 m/s or 1,235 kmph in air at 20 °C at sea level. The speed of sound depends on temperature and altitude : at the cruising altitude of a passenger jet (10,000 m), Mach 1 is about 1,062 kmph because the air is colder and thinner up there.

An average jogger runs at 8 to 10 kmph (2.2 to 2.8 m/s). Trained marathon runners average 18 to 20 kmph. Sprinters hit 35 to 37 kmph for short bursts : Usain Bolt peaked at 44.72 kmph (12.42 m/s) during his 100 m world record. Cars in Indian cities at 40 to 60 kmph easily outrun any sprinter.