Speed Converter

How the Speed Converter works

Every unit is defined as an exact fraction of a metre per second. A kilometre per hour is 1,000 m divided by 3,600 s. A mile per hour is 1,609.344 m per 3,600 s, which is exactly 0.44704 m/s. A foot per second is 0.3048 m/s, and a knot is one nautical mile (1,852 m) per hour, or 1,852/3,600 m/s.

Mach is not a fixed unit: it is a speed divided by the local speed of sound, which depends mainly on air temperature. This converter uses 343 m/s (1,234.8 km/h), the value for dry air at 20 °C at sea level. At the −56.5 °C of the lower stratosphere, where airliners cruise, the speed of sound is only about 295 m/s, so the same true airspeed is a higher Mach number.

Conversions multiply by the ratio of the two unit definitions, and results are rounded in decimal to the significant digits you choose.

How to use the Speed Converter

1. Type a speed in the Speed box, for example 100.
2. Choose the unit it is in from the From unit list.
3. Choose the precision in significant digits.
4. Read the table of every unit with its definition. Results update as you type.
5. Select Copy next to a value to copy it.

Example

Entering 100 with Kilometres per hour (km/h) selected gives:

Miles per hour (mph)       62.13711922
Metres per second (m/s)    27.77777778
Feet per second (ft/s)     91.13444153
Knots (kn)                 53.99568035
Mach                       0.08098477486

Common use cases

• Converting speed limits and car speeds between km/h and mph.
• Converting wind speeds between knots, m/s and km/h for sailing, flying or weather data.
• Converting physics or sensor readings in m/s or ft/s to everyday units.
• Getting a rough Mach number for an aircraft or projectile speed.

Frequently asked questions