Speed converter
Speed converter, no network, no rounding surprises.
Runs on your device. The file is never uploaded.
Speed converter handles four units: mps, kmh, mph and kn, with metres per second as the base. mph uses 0.44704, the exact figure implied by the statute mile. kmh and kn hold truncated decimals, 0.2777777778 and 0.5144444444, so the tenth digit of an answer is approximate rather than exact.
Questions
Which speed units are supported?
Four: mps for meters per second, kmh for kilometers per hour, mph for miles per hour and kn for knots. Meters per second is the base. mph uses the exact 0.44704 factor that follows from the statute mile, while kmh and kn are stored as the decimals 0.2777777778 and 0.5144444444.
Are the kmh and kn factors exact?
Those two are truncated decimals rather than exact fractions. A kilometer per hour is one over 3.6 meters per second and a knot is 1852 over 3600, and both repeat forever, so the table keeps ten decimal places. The difference shows up around the tenth digit of your answer, well below anything a speedometer or a chart cares about.
What exactly is a knot here?
One nautical mile per hour, stored as 0.5144444444 meters per second. It is the unit used for wind, sea and air speed, and it is faster than a mile per hour: 10 kn works out at roughly 11.5 mph. Convert kn to kmh if you want the number a car dashboard would show.
Can I convert a running pace like minutes per kilometer?
Not directly. Pace is time over distance and every unit here is distance over time, so the two are reciprocals rather than a ratio apart. Work out the speed first, for example 5 minutes per kilometer is 12 kmh, then convert that figure to whatever you need.
Why did it refuse my value?
The value must parse as a finite number, or you get "value must be a number". Leave the unit out of the field and use a dot for decimals. Both dropdowns have to be set, since neither from nor to has a default, and the result comes back as a single line naming both units.