Speed Converter
Convert km/h, mph, m/s, knots and feet per second.
Popular Speed conversions
All Speed units
About Speed
Speed covers five units and they map neatly onto five different worlds. Kilometers per hour is what road signs and car dashboards show in most of the world. Miles per hour is what they show in the United States and the United Kingdom. Meters per second is the SI unit and the one physics problems, wind readings and athletics data use. Knots are the unit of ships and aircraft. Feet per second shows up in US engineering and ballistics. Visitors arrive here because they are driving abroad and want to know what a limit really means, reading a weather report that gives wind in unfamiliar units, checking a flight or sailing speed, or working through a physics question. The pairs that get used most are km/h to mph, mph to km/h, m/s to km/h and knots to mph.
Speed is a compound unit, a distance divided by a time, which is what makes it interesting. Every conversion here is really two conversions happening together: the distance part changes and the time part changes, and the single factor on the page has already combined them. That is why converting meters per second to kilometers per hour is not a matter of just swapping meters for kilometers. The unit worth a closer look is the knot, which is one nautical mile per hour. Because the nautical mile is a navigation unit tied to the Earth's geometry rather than to the statute mile on road signs, a speed in knots is not the same as the same number in mph, and mixing them up is a real error in marine and aviation contexts. Wind speed is the other common source of confusion, because forecasts quote it in km/h, mph, m/s or knots depending on the country and the audience, and the same wind can look mild or alarming depending on which unit you assume.
Each pair page shows the formula it applied, a worked example, and a reference table covering the speeds people actually look up, such as common limits and typical wind readings. Everything is free, no sign-up is required, and the conversion runs entirely in your browser, so nothing is sent anywhere. If you have a distance and a time and need the speed itself rather than a unit change, work the distance out on the length converter first.
Frequently asked questions
What exactly is a knot?
A knot is one nautical mile per hour, and it is the standard speed unit at sea and in aviation. Because the nautical mile is a navigation unit based on the geometry of the Earth rather than the statute mile used on roads, a speed in knots does not equal the same number in miles per hour. Confusing the two is a genuine mistake in marine and flight contexts, so use the knots pages rather than assuming they are close enough.
Why is meters per second used in science but not on road signs?
Meters per second is the SI unit, so it is what physics equations, scientific instruments and wind measurement systems use, and it keeps formulas consistent with other SI units. It is a poor fit for driving because the numbers are small and awkward at road speeds, so countries use kilometers per hour or miles per hour instead. The m/s to km/h page bridges the two when you need to read a scientific figure in everyday terms.
Which countries use mph and which use km/h?
The United States and the United Kingdom post speed limits in miles per hour, and a handful of other territories do too. Nearly everywhere else uses kilometers per hour. This matters most when you drive abroad or rent a car, because a dashboard calibrated in one unit against signs in the other is easy to misread. The km/h to mph page and its reverse are the two most used in this category for exactly that reason.
Are these conversions free to use?
Yes. Every speed pair page is free, needs no account and has no limit on use. The maths runs in your browser, so nothing you type leaves your device. Each page also lists a reference table of common speeds, which is often quicker than entering a value when you just want a sense of scale.