Speed unit converter

Speed limits, wind forecasts and technical specifications use different units depending on the country and the field: km/h on the road, knots at sea, m/s in physics.

All speeds are converted to metres per second, the SI unit, and from there to the unit you select.

The knot has a geographic logic

A nautical mile equals one minute of arc of latitude on the Earth's surface. So a ship sailing at one knot covers exactly one minute of latitude per hour, which made position fixing immediate with chart and dividers. It is a unit born of navigation that survives because it remains the most practical at sea and in the air.

From km/h to m/s, divide by 3.6

It is the most useful conversion to remember. Ninety kilometres per hour is exactly twenty-five metres per second. It helps estimate braking distances: at that speed, every second of reaction time is twenty-five metres travelled before touching the pedal.

Air resistance grows with the square

Doubling speed multiplies by four the force that must be overcome. It is why fuel consumption soars on the motorway, why cyclists draft behind one another, and why speed records demand disproportionate power.

Speed of sound and the Mach number

In air at sea level and fifteen degrees, sound travels at about 1,235 km/h. That value falls with temperature, so Mach 1 is not a fixed speed but a ratio depending on conditions.