Speed Converter (km/h, mph, m/s, knots, Mach)

How to use

1. Type the speed you want to convert and pick its unit: km/h, mph, m/s, knots, feet per second or Mach.
2. Choose the unit you want the result in. The answer appears as you type, followed by the same speed in all six units at once.
3. Read the conversion factors below the table — and the note about Mach, which is not a fixed speed. Everything runs in your browser.

About this tool

Speed units are simple ratios of a distance to a time, so converting between them is one multiplication — provided you use the exact factors. This converter routes everything through metres per second: the value you type is multiplied by the factor of its own unit to get m/s, then divided by the factor of the target unit. The factors are the legal definitions rather than rounded shortcuts: 1 km/h is 1 ÷ 3.6 m/s, 1 mph is exactly 0.44704 m/s (from the international mile of 1,609.344 m), 1 knot is 1,852 ÷ 3,600 m/s because a nautical mile is exactly 1,852 m, and 1 ft/s is exactly 0.3048 m/s. That is why 100 km/h comes out as 62.137119 mph and 53.99568 knots instead of vaguer round figures.

Mach is the one unit here that is not a constant, and the tool says so on screen whenever you select it. Mach 1 is the local speed of sound, which depends on the temperature of the air: this converter uses 340.29 m/s, the ISA standard value for dry air at sea level and 15 °C. Climb and the air gets colder and thinner, and the speed of sound falls with it — roughly 295 m/s at a cruising altitude of 11 km, which is why an airliner flying Mach 0.85 is doing about 900 km/h up there rather than the 1,041 km/h the sea-level figure would suggest. Treat any Mach number in the table as a sea-level reference, not as an absolute speed.

Everyday uses: reading an American speed limit or a car review in mph and getting the km/h you actually drive, converting a running or cycling pace expressed in m/s, following a marine or aviation forecast quoted in knots, working out what a wind speed in km/h means for a boat, or checking the numbers in a physics exercise where SI units are mandatory. The full table also makes sanity checks easy — if a converted value looks wrong by a factor of roughly 3.6 or 1.6, you know which pair of units got swapped. All calculations run 100% in your browser, with nothing uploaded or stored.

The formula

Everything is converted through metres per second: m/s = value × factor of the source unit, and result = m/s ÷ factor of the target unit. Factors: 1 km/h = 1 ÷ 3.6 m/s · 1 mph = 0.44704 m/s · 1 kn = 1852 ÷ 3600 m/s ≈ 0.5144 m/s · 1 ft/s = 0.3048 m/s · Mach 1 = 340.29 m/s at sea level. Example: 100 km/h = 27.777778 m/s = 62.137119 mph = 53.99568 kn.

Frequently asked questions