Speed Converter

Speed Converter

Convert speed between km/h, mph, m/s, ft/s, knots and Mach with exact factors, the formula for each pair and a quick conversion table.

Value

From

–

Formula:

Significant figures

≈ means the result was rounded to the chosen number of significant figures.

Mach uses the speed of sound in the International Standard Atmosphere at sea level (15 °C): Mach 1 = 340.29 m/s ≈ 1,225 km/h. At altitude, where the air is colder, Mach 1 is slower.

{value} in every unit

Unit	Result

Quick conversion table: {from} to {to}

From	To

Common values

Reference	Value	Result

Unit definitions

Unit

How to use the speed converter

Type a speed in Value. A decimal point or a decimal comma both work.
Choose the starting unit in From and the target unit in To, for example kilometre per hour and mile per hour.
The result appears as you type, with the full line below it (“100 km/h ≈ 62.137119 mph”). Copy puts that line on your clipboard.
The Swap units button (⇄) reverses the conversion.
Use Significant figures to round more or less. A “≈” sign means the value shown has been rounded.

The page also lists your speed in every unit, a quick table for the selected pair (5, 10, 20… 130), everyday references such as a walking pace, the French motorway limit or an airliner’s cruise speed, and the value of each unit in metres per second.

Exact factors

All the factors except Mach are exact, because they derive from the exact definitions of the mile, the foot and the nautical mile:

1 km/h = 1,000 m ÷ 3,600 s = 1/3.6 m/s ≈ 0.27778 m/s.
1 mph = 1,609.344 m per hour = 0.44704 m/s = 1.609344 km/h.
1 ft/s = 0.3048 m/s = 1.09728 km/h.
1 knot = 1 nautical mile per hour = 1,852 m/h = 1.852 km/h ≈ 0.51444 m/s.

The quickest mental conversions: divide km/h by 3.6 to get m/s, and multiply mph by about 1.6 to get km/h.

About Mach

A Mach number is a speed divided by the local speed of sound, which is not a constant: it depends on the air temperature (about 20.05 × √T m/s, with T in kelvin). To give Mach a fixed value, this tool uses the International Standard Atmosphere at sea level, 15 °C: Mach 1 = 340.29 m/s, which is 1,225.044 km/h, about 761.2 mph or 661.5 knots.

At the cruise altitude of airliners, around 11,000 m, the standard air temperature is −56.5 °C and the speed of sound drops to about 295 m/s (1,062 km/h). An aircraft cruising at Mach 0.85 up there therefore flies at about 903 km/h of true airspeed, not the 1,041 km/h that the sea-level value gives. Use the Mach results as a sea-level reference, not for flight planning.

Where each unit is used

km/h: road signs and speedometers in most of the world.
mph: roads in the United States and the United Kingdom.
m/s: physics, weather (wind speed) and engineering.
knots: sailing, aviation and marine weather forecasts.
ft/s: ballistics and some US engineering fields.

Frequently asked questions

How do I convert km/h to mph?

Divide by 1.609344. For example, 100 km/h ÷ 1.609344 ≈ 62.14 mph and 130 km/h ≈ 80.78 mph. Choose kilometre per hour in From and mile per hour in To to see it directly.

How do I convert km/h to m/s?

Divide by 3.6, because an hour has 3,600 seconds and a kilometre 1,000 metres. 36 km/h is exactly 10 m/s.

What is a knot?

One nautical mile per hour, exactly 1.852 km/h or about 1.15 mph. The name comes from the knotted rope sailors let out behind the ship to measure its speed.

Why does Mach depend on altitude?

Because sound travels faster in warm air than in cold air. Mach 1 is 340.29 m/s in standard sea-level air at 15 °C, but only about 295 m/s in the −56.5 °C air of the lower stratosphere.

Can I enter a negative speed?

The conversion still works, but the tool shows a note: a speed is a magnitude, so enter the value without a sign.