Speed Converter — km/h, mph, Knots & Mach

How to use this speed converter

Enter a speed, choose the unit you have, and choose the unit you want. The result appears instantly with a table showing your speed in every supported unit. Use ⇄ to reverse the conversion.

Understanding the speed units

Kilometres per hour (km/h) is the road-speed standard in most countries, while miles per hour (mph) is used in the UK and the United States. One mph equals 1.60934 km/h, so a 70 mph motorway limit is about 113 km/h.

Metres per second (m/s) is the scientific standard and is common in weather reports for wind speed in many countries. The conversion is simple: multiply m/s by 3.6 to get km/h.

Feet per second (ft/s) appears in engineering, ballistics, and some US technical contexts.

Knots are used at sea and in aviation worldwide. One knot is one nautical mile per hour — exactly 1.852 km/h. Wind speeds in marine forecasts and aircraft speeds are given in knots.

Mach number expresses speed relative to the speed of sound. Mach 1 at sea level (15 °C) is about 1,225 km/h, but the speed of sound drops with altitude as air gets colder — so an airliner cruising at Mach 0.8 at 35,000 ft is flying slower in km/h than Mach 0.8 at sea level would suggest.

Frequently asked questions

How do I convert km/h to mph quickly?
Multiply by 0.621, or for a rough mental estimate, take a bit less than two-thirds. So 100 km/h ≈ 62 mph.

Why do ships and planes use knots instead of km/h?
Because a knot is tied to the nautical mile, which is based on the Earth's latitude grid — one minute of latitude per hour. This makes navigation charts and speed directly compatible.

How fast is Mach 1?
At sea level and 15 °C, about 1,225 km/h (761 mph). The exact value changes with air temperature, which is why our converter notes it uses the standard sea-level value.

What's a typical airliner cruising speed?
Around Mach 0.78–0.85, roughly 830–900 km/h ground speed depending on winds and altitude.

How many km/h is 1 m/s?
Exactly 3.6 km/h. A 10 m/s wind is a 36 km/h wind — fresh and strong, but not a storm.

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