Conversion factors
1 m/s = 2.237 mph = 3.6 km/h = 1.944 knots = 3.281 ft/s
1 knot = 1.151 mph = 1.852 km/h
Beaufort scale
| Force | Description | mph | knots | m/s |
|---|---|---|---|---|
| 0 | Calm | <1 | <1 | <0.5 |
| 1 | Light air | 1–3 | 1–3 | 0.5–1.5 |
| 2 | Light breeze | 4–7 | 4–6 | 1.6–3.3 |
| 3 | Gentle breeze | 8–12 | 7–10 | 3.4–5.4 |
| 4 | Moderate breeze | 13–18 | 11–16 | 5.5–7.9 |
| 5 | Fresh breeze | 19–24 | 17–21 | 8.0–10.7 |
| 6 | Strong breeze | 25–31 | 22–27 | 10.8–13.8 |
| 7 | Near gale | 32–38 | 28–33 | 13.9–17.1 |
| 8 | Gale | 39–46 | 34–40 | 17.2–20.7 |
| 9 | Strong gale | 47–54 | 41–47 | 20.8–24.4 |
| 10 | Storm | 55–63 | 48–55 | 24.5–28.4 |
| 11 | Violent storm | 64–72 | 56–63 | 28.5–32.6 |
| 12 | Hurricane force | 73+ | 64+ | 32.7+ |
Most small wind turbines start producing useful power around force 3 (gentle breeze) and reach rated output around force 6.
Frequently asked questions
What is 20 mph in knots?
20 mph is about 17.4 knots, or 8.9 m/s, which is force 5 on the Beaufort scale.
What wind speed is a gale?
Force 8, 39–46 mph (34–40 knots, 17.2–20.7 m/s).