Speed Converter
Five Ways to Say How Fast
Speed carries more unit baggage than almost any other quantity, because each field settled on its own convention and never moved. Road signs use km/h or mph. Ships and aircraft use knots. Physics uses m/s. Ballistics and fluid dynamics reach for ft/s. All five describe the same thing — distance over time — and all five are related by exact defined constants, so converting between them introduces no measurement uncertainty at all.
The Formula
The converter stores each unit as its equivalent in metres per second, then routes through that pivot:
(Factors are relative to 1 meter/second)
The factors themselves are derived, not measured. A knot is one nautical mile per hour, so its factor is 1852 ÷ 3600 = 0.5144444… m/s. Kilometres per hour is 1000 ÷ 3600 = 0.2777778… m/s. Miles per hour comes out at exactly 0.44704 m/s, because the mile is exactly 1609.344 m.
The Factors In Use
| Unit | Code | m/s per unit | Origin |
|---|---|---|---|
| Meters/Second | mps | 1 | SI derived unit |
| Kilometers/Hour | kph | 0.27777778 | 1000 ÷ 3600 |
| Miles/Hour | mph | 0.44704 | 1609.344 ÷ 3600 |
| Knots | knot | 0.51444444 | 1852 ÷ 3600 |
| Feet/Second | fps | 0.3048 | 0.3048 ÷ 1 |
Complete Cross-Conversion Table
One of each unit, in every other unit:
| 1 of… | m/s | km/h | mph | knots | ft/s |
|---|---|---|---|---|---|
| Meter/Second | 1 | 3.6 | 2.23693629 | 1.94384449 | 3.2808399 |
| Kilometer/Hour | 0.27777778 | 1 | 0.62137119 | 0.5399568 | 0.91134442 |
| Mile/Hour | 0.44704 | 1.609344 | 1 | 0.86897624 | 1.46666667 |
| Knot | 0.51444444 | 1.852 | 1.15077945 | 1 | 1.68780986 |
| Foot/Second | 0.3048 | 1.09728 | 0.68181818 | 0.5924838 | 1 |
Speed Limits Across the Border
| km/h | mph |
|---|---|
| 30 | 18.64113577 |
| 50 | 31.06855961 |
| 60 | 37.28227153 |
| 80 | 49.70969538 |
| 100 | 62.13711922 |
| 120 | 74.56454307 |
| 130 | 80.77825499 |
| mph | km/h |
|---|---|
| 20 | 32.18688 |
| 30 | 48.28032 |
| 40 | 64.37376 |
| 55 | 88.51392 |
| 60 | 96.56064 |
| 70 | 112.65408 |
| 80 | 128.74752 |
When the Unit Choice Matters
- Aviation and marine — airspeed, groundspeed and wind are all in knots, but runway lengths are in feet and visibility often in metres. Converting cleanly between knots and m/s is routine.
- Physics problems — kinematic and kinetic-energy equations expect m/s. A velocity handed to you in km/h has to be divided by 3.6 before it goes anywhere near an equation.
- Driving abroad — reading a 130 km/h autobahn limit as roughly 81 mph, or a 70 mph motorway limit as roughly 113 km/h.
- Sports measurement — pitch and serve speeds published in mph against radar equipment reporting km/h.
- Wind data — meteorological services variously report wind in knots, km/h, mph and m/s, sometimes within the same bulletin.
How to Use This Calculator
- Enter the speed figure in the Value field.
- Set the first dropdown to the unit that figure is currently expressed in.
- Set the second dropdown to the unit you want.
- Press Calculate. The explanation panel shows both factors and the division performed, so the result can be checked by hand.
Related Calculations
Need the distance side of the equation? The Length Converter covers metres, miles and nautical miles. For the force a moving fluid exerts, see the Pressure Converter.