Speed Converter

How fast, in any unit.

Convert between meters per second, kilometers per hour, miles per hour and knots.

How it works

Values are converted through meters per second. One km/h equals 1/3.6 m/s, one mph equals 0.44704 m/s, and one knot (one nautical mile per hour) equals about 0.5144 m/s.

When it helps

Handy for road-trip speed limits abroad, running paces, wind speeds or sailing and aviation.

Which unit is used where

Kilometers per hour are used on roads in most of the world, miles per hour in the US and UK, meters per second in science and weather data, and knots at sea and in aviation. Wind speed in forecasts may appear in any of these depending on the country.

To go from km/h to m/s, divide by 3.6; to go back, multiply by 3.6. That one rule covers most physics homework.

Worked examples

A 120 km/h motorway limit is about 74.6 mph. A 70 mph limit in the UK is about 112.7 km/h. A sprinter running 100 m in 10 seconds averages 10 m/s, which is 36 km/h. A wind of 20 knots is about 37 km/h or 10.3 m/s.

For runners, pace is often given as minutes per kilometer instead of speed. A 5:00 min/km pace equals 12 km/h, and 6:00 min/km equals 10 km/h.

Frequently asked questions

How fast is 100 km/h in mph?

About 62.1 mph.

Why do ships use knots?

A nautical mile relates to one minute of latitude, which makes navigation on charts easier.

Is a knot the same as a mile per hour?

No. A knot is one nautical mile per hour, about 1.15 mph or 1.852 km/h.

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