Miles per Hour to Kilometers per Hour

Miles per hour and kilometers per hour

A mile per hour is one international mile per hour: exactly 0.44704 m/s, or 1.609344 km/h. Speed limits and speedometers in the US and UK, and pitch speeds in baseball, use mph.

A kilometer per hour is 1,000 meters per 3,600 seconds: exactly 1/3.6 m/s. Speed limits, car speedometers and weather reports use km/h in most countries.

Worked example

Convert 65 mph: 65 × 1.609344 = 104.60736, so 65 miles per hour is 104.60736 kilometers per hour. Likewise 20 mph = 32.18688 km/h.

Estimating in your head

Multiply by 1.6 for a quick figure; it is off by about 0.6%. For 65 mph that gives 104 km/h, against 104.607 exactly.

Going the other way

To convert kilometers per hour to miles per hour, divide by 1.609344 (or multiply by 0.621371192237). The swap button between the boxes opens that page.

km/h = mph × 1.609344

1 mph = 0.44704 m/s and 1 km/h = ≈ 0.2777777778 m/s, both by definition, so the factor is their ratio: 1.609344 exactly. Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.