Speed Converter
Convert speed
Convert speed Runs locally in your browser
About the
The Speed Converter converts between metres per second, kilometres per hour, miles per hour, knots and Mach. All five are converted through metres per second, so any pair is one step rather than a chain of approximations, and the value updates as you type in either field. It is the quickest way to read a foreign speed limit, compare a boat's speed to a car's, or sanity-check a figure in a spec sheet.
Where people use the
- Reading a speed limit posted in a unit you do not use.
- Converting a boat or aircraft speed in knots into something comparable to a car.
- Checking a figure in a technical datasheet before quoting it.
- Comparing running or cycling speeds between metric and imperial records.
How to use the
- 1
Enter a value
Type into either field. Both directions are live, so you can type in the unit you have and read the one you want.
- 2
Choose the units
Pick a from unit and a to unit. Kilometres per hour to miles per hour is the default because it is the most common pair.
- 3
Read the result
The converted value appears in the other field, at full precision rather than rounded to a whole number.
- 4
Swap if needed
Switch the two units to convert back the other way without retyping.
Tips and best practices
- Remember knots are nautical miles per hour, not statute miles.
- Mach depends on air temperature; treat it as an approximation unless you know the conditions.
- Type into either field; both directions convert live.
Frequently asked questions
What is a knot?
One nautical mile per hour, which is 1.852 km/h. It is the standard unit at sea and in aviation, which is why boat and aircraft speeds are quoted in knots while road speeds are not.
What is Mach 1?
The speed of sound, roughly 343 metres per second in dry air at sea level and 20 degrees Celsius. The real value changes with temperature and altitude, so Mach is a ratio rather than a fixed speed.
Why is my mph to kmh figure slightly different from a road sign?
Because signs are rounded. 60 mph is 96.56 km/h exactly, and a sign will usually say 100 or 95.
How precise is the result?
The conversion factors are exact definitions except for Mach, which uses the standard sea-level speed of sound. Rounding happens only for display.