Speed Converter

How to use the speed Converter

1. Enter the value.
2. Choose the from from the list.
3. Choose the to from the list.
4. The result updates instantly as you type. There is no button to press.
5. Use Copy result to copy the figures, or Copy link to share a link that reopens the speed Converter with the same inputs.

How it works

Speed is distance divided by time, so every speed unit pairs a length unit with a time unit. Road speeds are posted in kilometres per hour in most countries and miles per hour in the United States and the United Kingdom. Science and engineering use metres per second, the SI unit. Ships and aircraft use knots, one nautical mile (1,852 m) per hour, which fits neatly with navigation charts based on latitude.

Because the length units are defined exactly, the conversions are exact too: 1 mph is exactly 0.44704 m/s, and 1 km/h is exactly 1/3.6 m/s. Dividing km/h by 3.6 gives m/s, which is handy for physics problems.

Mach number is speed relative to the speed of sound, which depends on air temperature rather than being a fixed figure. This converter uses 343 m/s, the speed of sound in dry air at 20 °C. At the colder temperatures where jets cruise, sound travels at about 295 m/s, so the same airspeed is a higher Mach number. The converter also shows how long it takes to cover a kilometre or a mile at the given speed, useful for pacing and travel times.

Formula

Example

A speed limit of 100 km/h is 100 ÷ 1.609344 = 62.14 mph, or 27.78 m/s. At that speed a kilometre takes 36 seconds. A ship cruising at 20 knots is moving at 37 km/h (23 mph), and an airliner at 900 km/h is at about Mach 0.73 by the sea-level figure.

Frequently asked questions