Bf 0 (< 1 kn): Sea like a mirror
Bf 1 (1 - 3 kn): Ripples with the appearance of scales are formed, but without foam crests
Bf 2 (4 - 6 kn): Small wavelets, still short but more pronounced: crests have a glassy
appearance and do not break
Bf 3 (7 - 10 kn): Large wavelets; crests begin to break; foam of glassy appearance; perhaps
scattered white horses
Bf 4 (11 - 16 kn): Small waves, becoming longer; fairly frequent white horses
Bf 5 (17 - 21 kn): Moderate waves, taking a more pronounced long form; many white horses
are formed (chance of some spray)
Bf 6 (22 - 27 kn): Large waves begin to form; the white foam crests are more extensive
everywhere (probably some spray)
Bf 7 (28 - 33 kn): Sea heaps up and white foam from breaking waves begins to be blown in
streaks along the direction of the wind
Bf 8 (34 - 40 kn): Moderately high waves of greater length; edges of crests begin to break into
the spindrift; the foam is blown in well-marked streaks along the direction of the wind
Bf 9 (41 - 47 kn): 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
Bf 10 (48 - 55 kn): Very high waves with long overhanging crests; the resulting foam, in
greater 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
shock-like; visibility affected
Bf 11 (56 - 63 kn): 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 white patches of
foam lying along the direction of the wind; everywhere the edges of the wave crests are blown
into froth; visibility affected
Bf 12 (> 63 kn): The air is filled with foam and spray; sea completely white with driving spray;
visibility very seriously affected
Bf 0, Bf 1, Bf 2, Bf 5, Bf 6, Bf 7and Bf 8 photo by R.R. Baxter (Crown Copyright)
Bf 3 photo by R. Palmer
Bf 4 photo by P.J. Weaver
Bf 9 photo by O.R. Bates
Bf 10 photo by J. Hodkinson
Bf 11 and Bf 12 photo by Post Office (Crown Copyright)
