Speed & Velocity Converter

Speed to Convert

Pick any two units — every other unit updates underneath.

Value

From

CONVERTED VALUE

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All units

The same quantity expressed every other way.

Exact: 1 mph = 0.44704 m/s · 1 knot = 1.852 km/h · 1 ft/s = 0.3048 m/s. Mach 1 = 340.29 m/s is the sea-level 15 °C convention, not a fixed speed.

Pace equivalent

Per kilometre—

Per mile—

Per 100 metres—

Distance in one hour—

Which of these are exact and which are conventions

The mile is exactly 1609.344 metres and the hour is exactly 3600 seconds, so mph ↔ km/h ↔ m/s are exact conversions with no rounding anywhere. The knot is exactly one nautical mile per hour, and the nautical mile is exactly 1852 metres, so that one is exact too.

Mach is different. It is the ratio of an object's speed to the local speed of sound, and sound travels faster in warm air than cold. At sea level and 15 °C the speed of sound is about 340.29 m/s, which is the figure used here. At 11,000 metres — normal cruising altitude, around −56 °C — it drops to roughly 295 m/s. The same aircraft at the same true airspeed has a noticeably higher Mach number up there, which is exactly why aircraft are flown to a Mach limit rather than a fixed speed.

Why pace is not the same as speed

Speed is distance per unit time; pace is time per unit distance. They are reciprocals, which means they do not average the same way. Run one mile at 10 min/mi and one at 6 min/mi and your average pace is 8 min/mi — but your average speed is not the average of 6 mph and 10 mph. This is the harmonic-mean trap that makes “average speed for the trip” questions surprisingly easy to get wrong.

Knots, and why aviation and shipping kept them

One nautical mile is about one minute of latitude, so travelling one knot for one hour moves you one minute of latitude north. That makes dead-reckoning navigation on a chart almost arithmetic-free, which mattered enormously before satellite positioning and still matters when it fails.

Frequently Asked Questions

Is 100 km/h exactly 62.137 mph?

It is 62.1371192237334 mph, and that figure is exact rather than measured, because the mile is defined as exactly 1609.344 metres. The display rounds it to a sensible number of significant figures.

Why does Mach 1 change with altitude?

Because the speed of sound depends on air temperature, not pressure. At sea level and 15 °C it is about 340.29 m/s; in the cold air at cruising altitude it falls to roughly 295 m/s, so the same true airspeed is a higher Mach number.

What is a knot, exactly?

One nautical mile per hour, where the nautical mile is exactly 1852 metres. That makes a knot exactly 1.852 km/h. Saying "knots per hour" is a common slip — the "per hour" is already inside the word.

Can I convert a running pace here?

Enter your speed and read the pace line underneath the result. Pace is the reciprocal of speed, so 12 km/h is 5:00 per kilometre and roughly 8:03 per mile.

Where these numbers come from

Sources

Official publications only. Links open the original document in a new tab.

National Institute of Standards and Technology The International System of Units (SI) Definitions of the SI base units
National Institute of Standards and Technology Special Publication 811 — Guide for the use of the SI Correct use and spelling of unit symbols
National Institute of Standards and Technology Office of Weights and Measures US authority on weights and measures