Waves at Chapel Porth Image by British Beaches CC BY-SA 3.0
The Beaufort scale is an empirical measure that relates wind speed to observed conditions at sea or on land. It is most commonly used in the Met Office marine forecast (commonly known as the shipping forecast).
| Beaufort number | Description | Wind speed | Wave height | Sea conditions | Land conditions |
|---|---|---|---|---|---|
| 0 | Calm | < 1 km/h | 0 m | Sea like a mirror | Smoke rises vertically. |
| < 1 mph | |||||
| < 1 knot | 0 ft | ||||
| < 0.3 m/s | |||||
| 1 | Light air | 1 - 5 km/h | 0 - 0.2 m | Ripples with appearance of scales are formed, without foam crests | Direction shown by smoke drift but not by wind vanes. |
| 1 - 3 mph | |||||
| 1 - 3 knots | 0 - 1 ft | ||||
| 0.3 - 1.5 m/s | |||||
| 2 | Light breeze | 6 - 11 km/h | 0.2 - 0.5 m | Small wavelets still short but more pronounced; crests have a glassy appearance but do not break | Wind felt on face; leaves rustle; wind vane moved by wind. Wind vanes begin to move. |
| 4 - 7 mph | |||||
| 4 - 6 knots | 1 - 2 ft | ||||
| 1.6 - 3.3 m/s | |||||
| 3 | Gentle breeze | 12 - 19 km/h | 0.5 - 1 m | Large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses | Leaves and small twigs in constant motion; light flags extended. |
| 8 - 12 mph | |||||
| 7 - 10 knots | 2 - 3.5 ft | ||||
| 3.4 - 5.5 m/s | |||||
| 4 | Moderate breeze | 20 - 28 km/h | 1 - 2 m | Small waves becoming longer; fairly frequent white horses | Raises dust and loose paper; small branches moved. |
| 13 - 18 mph | |||||
| 11 - 16 knots | 3.5 - 6 ft | ||||
| 5.5 - 7.9 m/s | |||||
| 5 | Fresh breeze | 29 - 38 km/h | 2 - 3 m | Moderate waves taking a more pronounced long form; many white horses are formed; chance of some spray | Small trees in leaf begin to sway; crested wavelets form on inland waters. |
| 19 - 24 mph | |||||
| 17 - 21 knots | 6 - 9 ft | ||||
| 8 - 10.7 m/s | |||||
| 6 | Strong breeze | 39 - 49 km/h | 3 - 4 m | Large waves begin to form; the white foam crests are more extensive everywhere; probably some spray | Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty. |
| 25 - 31 mph | |||||
| 22 - 27 knots | 9 - 13 ft | ||||
| 10.8 - 13.8 m/s | |||||
| 7 | High wind, moderate gale, near gale |
50 - 61 km/h | 4 - 5.5 m | Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind; spindrift begins to be seen | Whole trees in motion; inconvenience felt when walking against the wind. |
| 32 - 38 mph | |||||
| 28 - 33 knots | 13 - 19 ft | ||||
| 13.9 - 17.1 m/s | |||||
| 8 | Gale, Fresh gale |
62 - 74 km/h | 5.5 - 7.5 m | Moderately high waves of greater length; edges of crests break into spindrift; foam is blown in well-marked streaks along the direction of the wind | Twigs break off trees; generally impedes progress. |
| 39 - 46 mph | |||||
| 34 - 40 knots | 18 - 25 ft | ||||
| 17.2 - 20.7 m/s | |||||
| 9 | Strong/severe gale | 75 - 88 km/h | 7 - 10 m | High waves; dense streaks of foam along the direction of the wind; sea begins to roll; spray affects visibility | Slight structural damage (chimney pots and slates removed). |
| 47 - 54 mph | |||||
| 41 - 47 knots | 23 - 32 ft | ||||
| 20.8 - 24.4 m/s | |||||
| 10 | Storm, Whole gale |
89 - 102 km/h | 9 - 12.5 m | Very high waves with long overhanging crests; resulting foam in great patches is blown in dense white streaks along the direction of the wind; on the whole the surface of the sea takes on a white appearance; rolling of the sea becomes heavy; visibility affected | Seldom experienced inland; trees uprooted; considerable structural damage. |
| 55 - 63 mph | |||||
| 48 - 55 knots | 29 - 41 ft | ||||
| 24.5 - 28.4 m/s | |||||
| 11 | Violent storm | 103 - 117 km/h | 11.5 - 16 m | Exceptionally high waves; small- and medium-sized ships might be for a long time lost to view behind the waves; sea is covered with long white patches of foam; everywhere the edges of the wave crests are blown into foam; visibility affected | Very rarely experienced; accompanied by widespread damage. |
| 64 - 72 mph | |||||
| 56 - 63 knots | 37 - 52 ft | ||||
| 28.5 - 32.6 m/s | |||||
| 12 | Hurricane force | ≥ 118 km/h | ≥ 14 m | The air is filled with foam and spray; sea is completely white with driving spray; visibility very seriously affected | Devastation. |
| ≥ 73 mph | |||||
| ≥ 64 knots | ≥ 46 ft |