Speed Converter

The speed converter converts between miles per hour, kilometres per hour, metres per second, knots, and other speed units instantly. It is used by drivers, pilots, mariners, athletes, and engineers who work with speed measurements from different systems. Enter your speed value, choose your units, and convert with one click.

How to Use the Speed Converter

1. Enter the speed value you want to convert.
2. Select the unit you are converting from, such as mph or km/h.
3. Select the unit you are converting to.
4. Click Convert or read the result as it updates automatically.
5. For pace conversions used in running (minutes per kilometre or mile), switch to the pace mode if available.

The Formula

All speed conversions use metres per second (m/s) as the base unit:

Result = Input * (Value of input unit in m/s) / (Value of output unit in m/s)

Key conversion factors: 1 mph = 0.44704 m/s 1 km/h = 1/3.6 m/s (approximately 0.27778 m/s) 1 knot = 0.514444 m/s 1 foot per second = 0.3048 m/s 1 Mach (at sea level, 15°C) approximately 340.29 m/s

Common direct conversions: 1 mph = 1.60934 km/h 1 knot = 1.852 km/h 1 m/s = 3.6 km/h

Real-World Example

Convert 90 km/h to miles per hour (for a driver crossing from Europe to the UK).

1. Use the direct factor: 1 km/h = 1/1.60934 mph = 0.62137 mph
2. Multiply: 90 * 0.62137 = 55.92 mph

A speed limit of 90 km/h is approximately 56 mph. This is important for drivers moving between countries using different road sign systems, as speed limits must be interpreted correctly to avoid penalties.

Speed in Different Contexts

Speed is measured in different units depending on the context. Road transport typically uses mph in the UK and US, km/h almost everywhere else. Aviation uses knots for both airspeed and wind speed worldwide, with altitude in feet (except in Russia and China, which use metres). Maritime navigation uses knots. Athletics uses metres per second or pace (minutes per kilometre or mile). Physics and engineering often prefer metres per second, as it integrates cleanly with SI units in calculations of force, energy, and acceleration.

Frequently Asked Questions

What is a knot and why is it used in aviation and sailing? A knot is one nautical mile per hour (1.852 km/h). Nautical miles are based on degrees of latitude, making them geometrically meaningful for navigation on charts and in airspace. Using knots keeps speed directly linked to distance measured in nautical miles, simplifying navigation calculations.

What does Mach 1 mean? Mach 1 is the speed of sound, which varies with altitude and temperature. At sea level and 15°C, it is approximately 1225 km/h (761 mph or 340 m/s). Mach numbers above 1 are supersonic; below 1 are subsonic. Mach is used in aviation because aerodynamic effects depend on how fast an aircraft moves relative to the local speed of sound.

How do I convert running pace to speed? Running pace (minutes per kilometre) is the inverse of speed. To convert 5 min/km to km/h: divide 60 minutes by the pace. 60 / 5 = 12 km/h. To convert 8 min/mile to mph: 60 / 8 = 7.5 mph.

Is the speed of light ever needed in conversions? In physics and astronomy, speeds are sometimes expressed as a fraction of c, the speed of light (approximately 299,792,458 m/s or about 1.08 billion km/h). Particle physicists regularly express particle speeds as 0.9c, 0.99c, and so on.

Where the exact factors come from

The factors on this page are defined constants, not measurements. The international yard and pound agreement of 1959, signed by Australia, Canada, New Zealand, South Africa, the United Kingdom and the United States, fixed the international yard at exactly 0.9144 metres. A statute mile is 1,760 yards, so it is exactly 1,609.344 metres, and a mile per hour is exactly 0.44704 metres per second.

The nautical mile is exactly 1,852 metres by definition, adopted for international use in 1929. A knot is one nautical mile per hour, which is 1,852 divided by 3,600, or 0.5144444 recurring metres per second. A kilometre per hour is 1,000 divided by 3,600, or 0.27777 recurring metres per second.

None of those numbers carries a rounding error, which is why a conversion between any two of those units can be exact apart from the rounding applied at the end.

One speed written in five units

Each row of this table is a single speed expressed five ways. The rows come from dividing the input by the exact factor, with the results rounded for display.

The 90 km/h row is the useful checkpoint, because 90 divided by 3.6 gives exactly 25 metres per second. Two of the five figures are round on the same row, so a reader can confirm the rest of that row against them. The 100 km/h row is the one used for unit testing, because 100 divided by 1.609344 gives 62.1371 miles per hour and the rounding to 62.14 is visible at two decimals.

The speed of sound moves with air temperature

Mach 1 is not a fixed speed. The speed of sound in dry air follows from the square root of the product of the ratio of specific heats, the gas constant and the absolute temperature. For dry air the ratio of specific heats is 1.4 and the gas constant is 287.05 joules per kilogram per kelvin. Temperature has to be in kelvin, which is degrees Celsius plus 273.15.

The 15 C row reproduces the 1,225 km/h figure quoted in the FAQ above, which is the standard sea level value. The minus 56.5 C row is the temperature of the international standard atmosphere at 11 kilometres, which is roughly the cruising altitude of an airliner. The speed of sound falls from 1,225.05 to 1,062.24 km/h between those two rows, a drop of 13.3 percent.

That drop changes what a Mach number means at altitude. An aircraft flying at Mach 0.85 covers about 1,041 km/h at sea level in a standard atmosphere, and about 903 km/h at 11 kilometres. The two speeds differ by 26.3 percent, while the Mach number is identical. This is why a table of Mach numbers built at sea level gives the wrong ground speed by a wide margin for anything above the surface layer.

Pace is the reciprocal of speed

Running pace is measured in time per unit of distance, so it inverts the speed. The conversion keeps the seconds: 3,600 divided by the pace in seconds gives the speed in kilometres per hour.

The mile is the other side of the same conversion. A pace of 8 minutes per mile is 7.5 miles per hour, which is 12.07 kilometres per hour. Running at 12 kilometres per hour is a pace of 5:00 per kilometre, which is 8 minutes and 2.8 seconds per mile. Pace figures printed to a whole minute lose more information than speed figures do, because the reciprocal turns a small pace change into a larger speed change at the fast end of the table.

Rounding, and the figures that look like errors

Three statements on this page look approximate and are not.

The 0.514444 figure for a knot is a rounded print of a recurring decimal, because 1,852 divided by 3,600 does not terminate. The 1.852 km/h form of the same factor is exact, and it is the one to use in arithmetic.

The 299,792,458 metres per second figure quoted for the speed of light is exact by definition. The metre is defined as the distance light travels in 1 divided by 299,792,458 of a second, so that number is a definition rather than a measurement, and it carries no uncertainty.

The five-decimal factor of 0.62137 used in the worked example is a rounded form of 0.6213712. The difference per kilometre is 0.0000012 miles per hour, so at 90 km/h the rounded factor gives 55.9233 against an exact 55.9234. The gap is 0.0001 miles per hour, which no display on the page shows. Road speeds are safe with the rounded factor. Speeds above 1,000 km/h accumulate the error to about 0.0012 miles per hour, which is still below the precision of any published figure.

Also try these free tools:

• Unit Converter
• Length Converter
• Temperature Converter