Wind Speed Unit Converter
Convert wind speed between m/s, km/h, mph, knots, and Beaufort scale.
Includes Beaufort description and wind turbine cut-in reference.
Wind speed is measured in different units depending on the context. Meteorologists use m/s and km/h, sailors use knots, and forecasts often use the Beaufort scale.
Conversion factors:
- 1 m/s = 3.6 km/h = 1.944 knots = 2.237 mph
- 1 knot = 1.852 km/h = 0.514 m/s
- 1 mph = 1.609 km/h = 0.447 m/s
Beaufort Scale:
| Force | Speed (m/s) | Description | Sea state |
|---|---|---|---|
| 0 | 0–0.2 | Calm | Glassy |
| 1 | 0.3–1.5 | Light air | Ripples |
| 2 | 1.6–3.3 | Light breeze | Small wavelets |
| 3 | 3.4–5.4 | Gentle breeze | Large wavelets |
| 4 | 5.5–7.9 | Moderate breeze | Small waves |
| 5 | 8.0–10.7 | Fresh breeze | Moderate waves |
| 6 | 10.8–13.8 | Strong breeze | Large waves |
| 7 | 13.9–17.1 | Near gale | Sea heaps up |
| 8 | 17.2–20.7 | Gale | High waves |
| 9 | 20.8–24.4 | Strong gale | Very high waves |
| 10 | 24.5–28.4 | Storm | Exceptionally high waves |
| 11 | 28.5–32.6 | Violent storm | Phenomenal |
| 12 | 32.7+ | Hurricane force | Air filled with foam |
Wind turbine operating range:
- Cut-in speed: 3–4 m/s (turbine starts generating)
- Rated speed: 10–14 m/s (full rated power)
- Cut-out speed: 20–25 m/s (turbine shuts down to protect itself)
Why the power curve climbs so steeply
Available wind power follows P = ½ρAv³, so it goes with the cube of wind speed. Double the wind and you get eight times the power, not twice. That single fact drives almost every siting decision in the industry: a location averaging 7 m/s is worth roughly 1.6 times one averaging 6 m/s, which sounds like a small difference in the forecast and is an enormous one on the balance sheet.
It also explains the flat top on the chart above. Between cut-in and rated speed the curve rises as a cube, then the controller deliberately holds output at the generator’s rated power by pitching the blades. Everything above that line is energy the turbine chooses not to take, because the drivetrain cannot handle it.
No turbine captures all of it in any case. The Betz limit caps the theoretical maximum at 59.3% of the wind’s kinetic energy, since air has to keep moving to leave the rotor. Good modern machines reach roughly 45 to 50% in their best range.
A note on measurement height
Wind speed rises with height above ground, so a number is meaningless without one. Meteorological readings are standardised at 10 metres. A modern turbine hub sits at 80 to 120 metres, where the wind is meaningfully faster over open terrain and dramatically faster over rough ground or trees. Comparing a hub-height figure with an airport forecast is not comparing like with like.
Where the Beaufort scale came from
Francis Beaufort of the Royal Navy set it out in 1805, and its cleverness is that it needs no instrument at all. Every step is defined by something an officer could see: the shape of the waves, whether foam was streaking, how the sails behaved. That is why it survived into an age of anemometers. The sea-state column above is the original idea, and it still works from a beach.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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