Speed Converter
Convert between metres per second, km/h, mph, knots, Mach number, feet per second, speed of light, and more — all speed and velocity units instantly.
All Unit ConvertersAll conversions from 100 km/h
| Unit | Symbol | Value |
|---|
How this speed converter handles fourteen units, from feet per minute to the speed of light
Speed is distance over time, but the units people actually use range wildly in scale. A snail’s pace and a jet airliner and a beam of light are all speeds, just separated by many orders of magnitude. This converter treats them all the same way, by anchoring every unit to metres per second and letting two multiplications handle the rest.
Everything runs client side in your browser using plain JavaScript. Nothing you enter leaves your device.
Why metres per second is the anchor
Metres per second is the SI derived unit for velocity, built directly from the base units of length and time. Because it is a coherent SI unit, every other unit in the table only needs a single multiplier to express itself in metres per second, rather than needing dozens of separate cross conversion formulas.
| Unit | Symbol | m/s per unit |
|---|---|---|
| Metres per second | m/s | 1 |
| Centimetres per second | cm/s | 0.01 |
| Kilometres per hour | km/h | 0.277778 (1/3.6) |
| Kilometres per minute | km/min | 16.6667 |
| Kilometres per second | km/s | 1,000 |
| Miles per hour | mph | 0.44704 |
| Miles per minute | mi/min | 26.8224 |
| Miles per second | mi/s | 1,609.344 |
| Feet per second | ft/s | 0.3048 |
| Feet per minute | ft/min | 0.00508 |
| Knot | kn | 0.514444 |
| Mach (20°C, sea level) | Mach | 343.0 |
| Mach (11km altitude) | Mach(alt) | 295.07 |
| Speed of light (vacuum) | c | 299,792,458 |
The one truly fixed entry in the table
Speed of light
Set at exactly 299,792,458 metres per second, a defined constant since the 1983 redefinition of the metre itself in terms of the speed of light and a fixed time interval. Unlike Mach, this value never varies with conditions.
The knot
Defined as one nautical mile per hour, at exactly 0.514444 metres per second. It remains the standard speed unit in marine and aviation navigation worldwide, tied to the nautical mile’s basis in one minute of latitude.
Speed unit references
- BIPM SI Brochure defines the metre in terms of the fixed speed of light, 299,792,458 m/s, making that value exact by definition rather than measurement.
- FAA aeronautical references document standard atmosphere assumptions used for Mach number and altitude relationships in aviation.
- NIST SI derived units lists metres per second as the coherent SI unit for speed and velocity.
Speed in travel and in sport
Converting a car’s speedometer reading between km/h and mph when driving abroad, checking wind speed reported in knots against a metric weather app, translating a treadmill’s mph display into km/min pace for training logs, working out an aircraft’s cruising speed in Mach against its actual ground speed, and sanity checking a physics problem that mixes imperial and metric velocity units.
From the blog
Reading around units
Where measurement systems came from and why two of them still argue.
