Miles per hour to Kilometers per hour

About Miles per hour and Kilometers per hour

Miles per hour (mph): Derived from the mile (1,609.344 m exactly) and the hour; conventional speed unit in the US, UK, and a handful of other countries. Common uses: US road speed limits, US sports speeds (baseball pitches in mph), UK road signs, and most US vehicle dashboards.

Kilometers per hour (km/h): A practical unit derived from the kilometer (defined via the meter) and the hour (60 × 60 seconds). Common uses: Vehicle speed limits worldwide except in the US and a few other countries, train and aircraft cruise speeds (in metric contexts), and weather wind speeds.

How the conversion works

Speed is distance per unit time. 1 m/s = 3.6 km/h. 1 mph = 1.609344 km/h. 1 knot = 1.852 km/h (one nautical mile per hour).

The exact relationship is kilometers per hour = miles per hour × 1.60934271e+0, which the calculator at the top of this page applies in both directions. Type into either field and the other updates immediately.

When this conversion matters

Converting between miles per hour and kilometers per hour comes up wherever speed measurements move between systems — from one country's conventions to another's, from a scientific reference to a practical specification, or from one industry's working unit to another's. The calculator and reference table above cover the everyday range; for unusual values you can type any number into either field.