Beaufort Scale Page

Beaufort number Description Wind speed Wave height Sea conditions Land conditions Associated warning flag
0 Calm < 1 knot
< 1 mph
< 2 km/h
< 0.5 m/s
0 ft (0 m) Sea like a mirror Smoke rises vertically.
1 Light air 1-3 knots 0-1 ft Ripples with appearance of scales are formed, without foam crests Direction shown by smoke drift but not by wind vanes.
1-3 mph
2-5 km/h 0-0.3 m
0.5-1.5 m/s
2 Light breeze 4-6 knots 1-2 ft 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.
4-7 mph
6-11 km/h 0.3-0.6 m
1.6-3.3 m/s
3 Gentle breeze 7-10 knots 2-4 ft 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
12-19 km/h 0.6-1.2 m
3.4-5.5 m/s
4 Moderate breeze 11-16 knots 3.5-6 ft Small waves becoming longer; fairly frequent white horses Raises dust and loose paper; small branches moved.
13-18 mph
20-28 km/h 1-2 m
5.5-7.9 m/s
5 Fresh breeze 17-21 knots 6-10 ft 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
29-38 km/h 2-3 m
8-10.7 m/s
6 Strong breeze 22-27 knots 9-13 ft 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. Gale pennant
25-31 mph
39-49 km/h 3-4 m
10.8-13.8 m/s
7 High wind,
moderate gale,
near gale
28-33 knots 13-19 ft 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. Gale pennant
32-38 mph
50-61 km/h 4-5.5 m
13.9-17.1 m/s
8 Gale,
fresh gale
34-40 knots 18-25 ft 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. Gale pennant
Gale pennant
39-46 mph
62-74 km/h 5.5-7.5 m
17.2-20.7 m/s
9 Strong/severe gale 41-47 knots 23-32 ft 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). Gale pennant
Gale pennant
47-54 mph
75-88 km/h 7-10 m
20.8-24.4 m/s
10 Storm
whole gale
48-55 knots 29-41 ft 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. Storm Warning
55-63 mph
89-102 km/h 9-12.5 m
24.5-28.4 m/s
11 Violent storm 56-63 knots 37-52 ft 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. Storm Warning
64-72 mph
103-117 km/h 11.5-16 m
28.5-32.6 m/s
12 Hurricane force ≥ 64 knots  ≥ 46 ft The air is filled with foam and spray; sea is completely white with driving spray; visibility very seriously affected Devastation. Storm Warning

Storm Warning
≥ 73 mph
≥ 118 km/h ≥ 14 m
≥ 32.7 m/s