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Speed Converter
Convert km/h, mph, metres per second and knots for driving, flying and sailing.
You are renting a car in a country that posts speed limits in km/h and your dashboard defaults to mph. Sixty on the sign and sixty on your speedometer are not remotely the same speed, and that gap is exactly the kind of mistake that gets a speeding ticket.
Speed units compared
| Unit | In km/h | In mph | In m/s |
|---|---|---|---|
| 1 km/h | 1 | 0.621 | 0.278 |
| 1 mph | 1.609 | 1 | 0.447 |
| 1 m/s | 3.6 | 2.237 | 1 |
| 1 knot | 1.852 | 1.151 | 0.514 |
Why sailors measure speed in knots
A knot is one nautical mile per hour, and it is defined exactly: 1.852 km/h, fixed by international agreement in 1929. The unit gets its name from an old, literal method — sailors would throw a wooden board tied to a rope with evenly spaced knots over the stern, let it drag, and count how many knots paid out while a sandglass ran for a set time. However many knots slipped through their hands in that interval was the ship’s speed, and the name outlived the method by centuries.
Knots remain standard in shipping and aviation today because a nautical mile is tied to the Earth’s geometry — one minute of latitude — which makes it directly useful for chart navigation in a way that kilometres and miles are not.
Where each unit is standard
- km/h — most of the world’s road signs and speedometers.
- mph — road speeds in the United States, the United Kingdom, and a handful of other countries.
- m/s — scientific and engineering contexts: wind speed, physics problems, sports timing.
- Knots — maritime navigation and aviation, worldwide, regardless of the country underneath.
A couple of reference points worth keeping in mind
Highway driving speed of 100 km/h is about 62 mph. A brisk human running pace, around 15 km/h, is roughly 4.2 m/s. The cruising speed of a commercial airliner, often quoted around 900 km/h, is close to 486 knots — pilots and air traffic control talk in knots specifically so that a plane’s speed and a ship’s speed and a chart’s distance scale all use the same underlying unit.
Speed conversion questions
How do I convert mph to km/h?
Multiply by 1.60934. So 70 mph, a common US and UK motorway speed, converts to about 112.7 km/h.
Is a knot the same as a mile per hour?
No, though they are close. A knot is 1.852 km/h, slightly faster than a statute mile per hour at 1.609 km/h. Confusing the two on a boat or aircraft would introduce a real, compounding navigation error over a long distance.
Why does aviation use knots instead of km/h or mph?
Because aeronautical charts are built on latitude and longitude, and a nautical mile is defined as one minute of latitude. Using knots lets pilots read speed, distance and time directly off the same chart without converting units.
What is m/s used for in everyday life?
Mostly science and engineering: wind speed forecasts, the physics behind car crash tests, and sports science timing sprinters. It is the SI unit for speed, so it is the default in any calculation rooted in physics.
How fast is the speed of sound in these units?
At sea level and 20°C, sound travels at roughly 343 m/s, which is about 1,235 km/h or 767 mph. That figure drops at altitude as the air gets colder, which is why aircraft Mach numbers are not a fixed speed in km/h.
