Specification of the Beaufort Scale or Wind Force




of wind

Sea Criterion

Mean speed

in knots

0 Calm Sea like a mirror. Less than 1
1 Light air Ripples with the appearance of scales are formed but without foam crests. 1 - 3
2 Light breeze Small wavelets, still short but more pronounced. Crests have a glassy appearance and do not break. 4 - 6
3 Gentle breeze Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses. 7 - 10
4 Moderate breeze Small waves, becoming longer, fairly frequent white horses. 11 - 16
5 Fresh breeze Moderate waves, taking a more pronounced long form, many white horses are formed. (Chance of some spray.) 17 - 21
6 Strong breeze Large waves begin to form; the white foam crests are more extensive everywhere. (Probably some spray.) 22 - 27
7 Near gale Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind. 28 - 33
8 Gale Moderately high waves of greater length; edges of crests begin to break into spindrift. The foam is blown in well-marked streaks along the direction of the wind. 34 - 40
9 Severe gale High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility. 41 - 47
10 Storm Very high waves with long overhanging crests. The 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 a white appearance. The tumbling of the sea becomes heavy and shocklike. Visibilty affected. 48 - 55


Violent storm Exceptionally high waves. (Small and medium-sized ships might be for a time lost to view behind the waves.) The sea is completely covered with long patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibilty affected. 56 - 63


Hurricane The air is filled with foam and spray. Sea completely white with driving spray; visibilty very seriously affected. 64 +