Speed Converter
Enter a value to instantly convert between speed units.
Speed conversions are most often needed when traveling internationally — reading a speed limit sign in km/h when your car's speedometer shows mph, or understanding wind speed and aviation/maritime speeds given in knots. Because speed combines a distance unit and a time unit, there are more possible unit combinations than in most categories, but a handful (km/h, mph, m/s, and knots) cover the vast majority of real-world use.
1 Kilometer per Hour = 0.6214 Mile per Hour
Key Formulas
Kilometer per Hour → Mile per Hour
mph = km/h × 0.621371Mile per Hour → Kilometer per Hour
km/h = mph × 1.60934Knot → Mile per Hour
mph = kn × 1.15078Mile per Hour → Knot
kn = mph × 0.868976Popular Conversions
All Speed Conversions
About Speed Conversions
History & Background
Kilometers per hour and miles per hour both follow naturally from their respective distance units (the kilometer and the mile) divided by the hour, which has been the standard unit of everyday time for millennia. Meters per second is the SI-derived unit, used in physics and engineering because it pairs the base units of length and time directly, without the conversion factors that 'per hour' units introduce. The knot — one nautical mile per hour — has nautical and aviation origins: it relates directly to a minute of latitude, making it convenient for navigation calculations that involve the Earth's geometry.
How to Use This Converter
Enter a speed value and select your starting and target units for an instant conversion. For road travel, km/h and mph are the most relevant; for science and engineering, m/s is standard; for aviation, sailing, and weather reports, knots are common. The conversion factors account for both the distance and time components of each unit.
Frequently Asked Questions
Why do speed limit signs use km/h in most countries but mph in the US and UK?
This follows directly from each country's choice of distance unit for road signage — countries that use kilometers for road distances also use km/h for speed, and the US and UK (which use miles for road distances) use mph. The UK is a partial exception: it uses metric units for most measurements but has retained miles and mph for road signage.
What is a knot and why is it used for ships and aircraft?
A knot is one nautical mile (1,852 meters) per hour. It's used in maritime and aviation contexts because a nautical mile corresponds to one minute of latitude on the Earth's surface, which makes navigation calculations involving charts and coordinates more direct than they would be using land-based distance units like miles or kilometers.
How fast is 100 km/h in mph?
100 km/h is approximately 62.1 mph. A useful rough approximation for quick mental conversion is that km/h is about 0.6 times mph (or mph is about 1.6 times km/h) — close enough for a quick sanity check, though the converter on this page gives the precise figure for anything where accuracy matters.
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