Wind
The Beaufort Scale for Sailors — Force 0 to 12 Explained
Published · Last checked October 2026
The Beaufort scale describes wind strength from force 0 (calm, under 1 knot) to force 12 (hurricane force, 64 knots or more) by its effect on the sea. Force 4 (11 to 16 knots) is a good sailing breeze, force 6 (22 to 27 knots) is often called a 'yachtsman's gale', and force 8 (34 to 40 knots) is a gale. Forecasts give mean wind; gusts can be much stronger.
| Force | Name | Knots | Waves | On a 10 m yacht |
|---|---|---|---|---|
| 0 | Calm | Under 1 | Flat | Motor |
| 1 | Light air | 1–3 | 0.1 m | Drifting |
| 2 | Light breeze | 4–6 | 0.2 m | Gentle sailing |
| 3 | Gentle breeze | 7–10 | 0.6 m | Ideal for learning |
| 4 | Moderate breeze | 11–16 | 1 m | Great sailing; small boats reef |
| 5 | Fresh breeze | 17–21 | 2 m | Reef; wet upwind |
| 6 | Strong breeze | 22–27 | 3 m | Two reefs; experienced crews |
| 7 | Near gale | 28–33 | 4 m | Deep reefs; stay in harbour unless prepared |
| 8 | Gale | 34–40 | 5.5 m | Do not set out |
| 9 | Severe gale | 41–47 | 7 m | Storm tactics |
| 10 | Storm | 48–55 | 9 m | Dangerous |
| 11 | Violent storm | 56–63 | 11.5 m | Dangerous |
| 12 | Hurricane force | 64+ | 14 m+ | Extreme |
Mean wind vs gusts
Forecast forces are average speeds. Gusts can be 30 to 50 per cent stronger, more in showers and off high land. Reef for the gusts you expect, not the average.
Why the sea matters as much as the wind
Beaufort's wave heights are for the open sea after the wind has blown for a long time over a long fetch. Close to a weather shore the sea will be flatter. Against a strong tidal stream, over shallows or off headlands, the same wind can make short, steep, breaking seas.
See each force visualised with the interactive Beaufort scale and keep the Beaufort cheat sheet by the chart table.