What next?
Speed converts, then usually becomes a pace or an energy figure.
How to use this converter
- Enter a speed and its unit.
- Pick the unit to convert to.
- Read the converted speed and equation.
The conversions worth memorising
Roughly, 100 km/h is 62 mph, and 1 m/s is about 3.6 km/h. Knots (nautical miles per hour) are used in aviation and sailing: one knot is about 1.15 mph or 1.85 km/h.
For running, pace in minutes per km or mile is usually more useful than raw speed — the pace calculator handles that.
What your result means
A speed is a distance divided by a time, so converting one means converting both parts. Going from mph to km/h only changes the distance unit, which is why the factor is a simple 1.609; going from km/h to m/s changes distance and time together, which is why the factor is the less memorable 1 ÷ 3.6.
Knots deserve special care. One knot is one nautical mile per hour, and a nautical mile is 1,852 m — a distance defined by the Earth's geometry rather than by land measure. That is why aviation and marine speeds never convert to round numbers, and why a "10 knot" forecast is 18.5 km/h rather than the 16.1 km/h you would get by treating it as a statute mile.
Why this one is different
Knots are included alongside mph, km/h, m/s and ft/s, because a wind forecast, a boat log and a car speedometer rarely share a unit. The line under the answer gives the factor in both directions, which is the number worth remembering for the pair you convert most.
Reading a speed correctly depends on knowing which one is quoted
Three different speeds get quoted as though they were the same. Indicated speed is what your instrument shows, and car speedometers are legally allowed to over-read but never under-read, so most sit a few percent high. Ground speed is what GPS measures and what a speed camera enforces. Average speed is total distance over total time, including every stop — which is why a journey at a steady 70 mph can average 48.
That last distinction is the one that breaks journey planning. Adding a fifteen-minute stop to a two-hour drive drops the average by more than 10 percent, and average-speed enforcement zones measure exactly that, not your instantaneous reading between cameras.
For converting between the units themselves, two anchors are worth memorising: multiply metres per second by 3.6 for km/h, and a knot is 1.852 km/h, being one nautical mile — one minute of latitude — per hour. The nautical mile survives in aviation and shipping precisely because it maps onto the globe's coordinate grid, which is a genuinely useful property when you are navigating rather than just measuring.
Frequently asked questions
How do I convert km/h to mph?＋
Multiply km/h by 0.621. So 50 km/h is about 31 mph, and 100 km/h is about 62 mph.
What is a knot?＋
A knot is one nautical mile per hour, equal to about 1.852 km/h. It is the standard speed unit for ships and aircraft.
How do I convert a pace into a speed?＋
Divide 60 by the pace in minutes per kilometre. A 5:00/km pace is 60 divided by 5, or 12 km/h.
What speed is the speed of sound?＋
About 343 m/s in dry air at 20 C, which is roughly 1,235 km/h or 767 mph. It falls as air temperature drops, which is why altitude matters in aviation.
Why do car speedometers read high?＋
Regulations allow a speedometer to over-read but never under-read, so most show a few percent above true speed. A GPS reading is usually closer to the truth.
How do I convert m/s to km/h in my head?＋
Multiply by 3.6. Ten metres per second is 36 km/h, which is a useful anchor to check any converted figure.
Related converters
Conversion reference
A knot is one nautical mile per hour, and a nautical mile is one minute of latitude — which is why it survives in aviation and shipping.
Worked example
A 60 mph speed limit in km/h and m/s:
60 × 1.609344 = 96.56 km/h
96.56 ÷ 3.6 = 26.82 m/s
Handy approximations: multiply mph by 1.6 for km/h, and divide km/h by 3.6 for m/s (that one is exact).
Assumptions & limitations
Speed conversion is exact; interpreting speed is not:
- These are all average or instantaneous speeds — scalar quantities. Velocity also has direction, and the two are not interchangeable in physics problems.
- Physics calculations almost always expect m/s. Feeding km/h into a kinetic energy or momentum formula gives an answer wrong by a factor of 12.96.
- Speedometers are legally allowed to over-read (never under-read) in the UK and EU, typically by a few percent.
- Wind speed is often quoted in knots or on the Beaufort scale, which is a description of conditions rather than a linear unit.