The Beaufort Scale of Wind Force

Force	Description	On Land	On Sea	Speed (kn)
0	Calm	Smoke rises vertically	Sea like a mirror	0
1	Light Air	Smoke drifts. Wind Vane still.	Small ripples.	1 - 3
2	Light breeze	Wind felt on face. Leaves rustle. Wind vane moves.	Small wavelets, glassy crests.	4 - 6
3	Gentle breeze	Leaves and small twigs in constat motion. Light flag extended.	Large wavelets. Crests break. Glassy foam.	7 - 10
4	Moderate breeze	Raises dust. Moves small branches.	Small waves but fairly frequent "white horses".	11 - 16
5	Fresh breeze	Small trees in leaf begin to sway.	Moderate waves, more pronounced long form. Many "white horses".	17 - 21
6	Strong breeze	Large branches in motion.	Large waves. Extensive foam crests. Probably some spray.	22 - 27
7	Near Gale	Whole trees in motion.	Sea heaps up. White foam streaks along wind.	28 - 33
8	Gale	Breaks twigs off trees. Impedes progress.	Moderately high waves of greater strength; edges of crests begin to break into spindrift. Foam blown in well marked streaks along wind.	34 - 40
9	Severe Gale	Slight structural damage possible. Tree branches may break.	High waves. Dense foam streaks along wind. Wave crests begin to topple and roll over. Spray may affect visibility.	41 - 47
10	Storm	Seldom experienced inland. Trees uprooted. Considerable structural damage.	Very high waves with long ovehanging crests. Dense large patches of foam blown along wind. Sea surface white. Visibility reduced.	48 - 55
11	Violent Storm	Rarely experienced. Widespread damage.	Exceptionally high waves. Sea covered with long white patches of foam along wind. Everywhere edges of wave crests blown into froth. Visibility much reduced.	56 - 63
12	Hurricane	Widespread severe damage.	Air filled with foam and spray. Sea completely white with driving spray. Visibility seriously affected.	64 +