Beaufort Wind Scale
Devised by British Rear-Admiral, Sir Francis Beaufort in 1805
based on observations of the effects of the wind
Beaufort Wind Speed Wave WMO* Effects observed on the sea
number height description
(force) (feet)  
  knots mph    
0 under 1 under 1 - Calm Sea is like a mirror
1 1 - 3 1 - 3 0.25 Light air Ripples with appearance of scales; no foam crests
2 4 - 6 4 - 7 0.5 - 1 Light breeze Small wavelets; crests of glassy appearance, not breaking
3 7 - 10 8 - 12 03-Feb Gentle breeze Large wavelets; crests begin to break; scattered whitecaps
4 11 - 16 13-18   Moderate breeze Small waves, becoming longer; numerous whitecaps
5 17-21 19-24 08-Jun Fresh breeze Moderate waves, taking longer form; many whitecaps; some spray
6 22-27 25-31 9-13 Strong breeze Larger waves forming; whitecaps everywhere; more spray
7 28-33 32-38 13-19 Near gale Sea heaps up; white foam from breaking waves begins to be blown in streaks
8 34-40 39-46 18-25 Gale Moderately high waves of greater length; edges of crests begin to break into spindrift; foam is blown in well-marked streaks
9 41-47 47-54 23-32 Strong gale High waves; sea begins to roll; dense streaks of foam; spray may begin to reduce visibility
10 48-55 55-63 29-41 Storm Very high waves with overhanging crests; sea takes white appearance as foam is blown in very dense streaks; rolling is heavy and visibility is reduced
11 56-63 64-72 37-52 Violent storm Exceptionally high waves; sea covered with white foam patches; visibility further reduced
12 64 and over 73 and over 45 and over Hurricane Air filled with foam; sea completely white with driving spray; visibility greatly reduced
* World Meteorological Organization