Speed Unit Converter
| Unit | Symbol | = base units |
|---|---|---|
| meter per second | m/s | 1 m/s |
| kilometer per hour | km/h | 0.277777778 m/s |
| mile per hour | mph | 0.44704 m/s |
| knot | kn | 0.514444444 m/s |
| foot per second | ft/s | 0.3048 m/s |
| mile per second | mi/s | 1,609.344 m/s |
| mach (sea level) | Ma | 340.3 m/s |
| speed of light | c | 299,792,458 m/s |
| foot per minute | ft/min | 0.00508 m/s |
| inch per second | in/s | 0.0254 m/s |
How to Use
Overview
The same speed appears as km/h on a dashboard, as pace in a running app, as knots on a ship or aircraft, as m/s in a weather bulletin, as ft/min on a conveyor, and as Mach above the speed of sound. Built on metres per second with ten units, this table turns 100 km/h into 27.7778 m/s and 62.1371 mph at a glance, and keeps one knot at 1.852 km/h, the same definition that fixes the nautical mile. A single leg logged in three different units needs one shared base before any comparison is fair. Two traps are worth naming. The knot is not an imperial oddity but a direct consequence of the nautical mile, so a vessel making twenty knots covers twenty nautical miles in an hour and about 37 kilometres, which is why harbour charts quote knots rather than km/h. Mach is worse, because it is a ratio against the local speed of sound: the same Mach 0.8 is roughly 850 km/h at sea level but nearer 950 km/h in the cold air at cruise altitude, so a single fixed conversion only holds near the reference temperature used here. Wind reports use metres per second while sailing uses knots for the same air.
Features
- Ten units in one view: m/s, km/h, mph, knot, ft/s, mi/s, Mach, speed of light, ft/min, in/s
- Road and sea line up: one knot is 1.852 km/h, that is one nautical mile per hour
- Metric and imperial side by side: 100 km/h is 27.7778 m/s or 62.1371 mph
- Mach uses the 15 C sound speed: about 340.3 m/s or 1,225.08 km/h
- ft/min and in/s cover fans, conveyors and machining line speeds
- Expression input, zero to eight decimals, batch conversion and TXT or CSV export
How to use
- Enter a speed or an expression, for example 120 or 100+20
- Choose the source unit: km/h for road speed, knots for vessels, m/s for weather
- Leave the target empty for all ten results, or pin one such as mph or Mach
- For running, convert pace to km/h first instead of comparing pace with speed directly
- Paste several lines and export CSV for a speed log or a voyage record
Notes
- Ten speed units run from metre per second and kilometre per hour through mph, knots, feet per second and mile per second to Mach, light speed, feet per minute and inches per second, with metres per second as the base.
- One metre per second is 3.6 km/h, a knot 1.852 km/h and a mile per hour 1.609344 km/h, so marine use takes knots while roads take km/h or mph and the unit must be stated.
- Mach is relative: at the 15 C sound speed of 340.3 m/s it is about 1,225.08 km/h, and colder air aloft lowers that figure for the same Mach number.
- Light speed uses the defined 299,792,458 m/s, so results are order-of-magnitude only; c and Mach are reference scales rather than ordinary speed units.
- Feet per second, per minute and inches per second serve machinery and wind work; CSV exports numbers and units must be unified before comparison.
- Pace in minutes per kilometre is not a speed unit; convert it to km/h before comparing, this tool does not output pace
- The conversion assumes constant speed and ignores acceleration, drag and wheel diameter, so speedometer error is out of scope
- ft/min and in/s serve conveyors, fans and machining, with 1 ft/min = 0.00508 m/s