Beaufort, Francis

Beaufort  Wind  Scale    

wind scale

Wind effects observed on sea

Beaufort  #

WMO  description



wind speed

wind speed

Wind effects observed on land


Sea surface smooth and mirror-like.


< 1 knot

< 1 mph

< 1 km/h

< 0.5 m/s


Calm; smoke rises vertically.


Ripples with the appearance of scales are formed, but without foam crests.


1--3 knots

1--3 mph

1--5 km/h

0.5--1.5 m/s

Light air

Direction of wind shown by smoke drift, but not by wind vanes.


Small wavelets, still short, but more pronoun- ced; crests have a glassy appearance and do not break.


4--6 knots

4--7 mph

6--11 km/h

1.6--3.0 m/s

Light breeze

Wind felt on face, leaves rustle, vanes begin to move.


Large wavelets; crests begin to break; foam of glassy appearance; perhaps some scattered whitecaps (white foam crests).


7--10 knots

8--12 mph

12--19 km/h

3.1--5.1 m/s

Gentle breeze

Leaves and small twigs in constant motion; wind extends light flag.


Small waves (1-4 ft), becoming longer; fairly frequent whitecaps.


11--16 knots

13--18 mph

20--28 km/h

5.2--8.2 m/s

Moderate breeze

Dust, leaves, and loose paper lifted, small tree branches move.


Moderate waves (4-8 ft), taking a more pronoun- ced long form; many whitecaps; some spray.


17--21 knots

19--24 mph

29--38 km/h

8.3--10.8 m/s

Fresh breeze

Small trees in leaf begin to sway; crested wavelets form on inland waters.


Larger waves (8-13 ft) begin to form; whitecaps common; more spray.


22--27 knots

25--31 mph

39--49 km/h

10.9--13.9 m/s

Strong breeze

Large tree branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty.


Sea heaps up; waves of ~13 ft; white foam from breaking waves begins to be blown in streaks along the direction of the wind


28--33 knots

32--38 mph

50--61 km/h

14.0--17.0 m/s

Near gale

Whole trees in motion; resistance felt when walking against the wind.


Moderately high (13-20 ft) waves of greater length; edges of crests begin to break into spindrift; foam is blown in well-marked streaks along the direction of the wind.


34--40 knots

39--46 mph

62--74 km/h

17.1--20.5 m/s


Breaks twigs off trees; generally impedes motion against wind.


High waves (20 ft); crests of waves begin to topple, tumble and roll over; dense streaks of foam along the direction of the wind; spray may reduce visibility.


41--47 knots

47--54 mph

75--88 km/h

20.6--24.2 m/s

Strong gale  (Severe gale)

Slight structural damage occurs, chimney-pots and slate blows off roofs.


Very high (20-30 ft) waves with overhanging crests; sea surface takes white appearance as foam is blown in very dense streaks along the direction of the wind; tumbling (rolling) of the sea becomes heavy and shock like; lowered visibility.


48--55 knots

55--63 mph

89--102 km/h

24.3--28.3 m/s


Seldom experienced on land, trees broken or uprooted, considerable structural damage occurs.


Exceptionally high (30-45 ft) waves; small and medium-size ships might be for a time lost to view behind the waves; sea completely covered with long white patches of foam lying along the direction of the wind; edges of the wave crests blown into froth; visibility further reduced.


56--63 knots

64--72 mph

103--117 km/h

28.4--32.4 m/s

Violent storm

Very rarely experienced on land; accompanied by wide-spread damage.


Air filled with foam and spray; waves over 45 ft; sea completely white with driving spray; visibility greatly reduced


>= 64 knots

>= 73 mph

>= 118 km/h

>= 32.5 m/s



UPDATED : 2004-11-07


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