Wind speed

Estimating wind speed

Beaufort number

Knots

Mph

Meters per second

Km per hour

Seaman's term

World meteorological organization (1964)

Effects observed at sea

Effects observed on land

0

under 1

under 1

0.0-0.2

under 1

Calm

Calm

Sea like mirror.

Calm; smoke rises vertically.

1

1-3

1-3

0.3-1.5

1-5

Light air

Light air

Ripples with appearance of scales; no foam crests.

Smoke drift indicates wind direction; vanes do not move.

2

4-6

4-7

1.6-3.3

6.11

Light Breeze

Light Breeze

Small wavelets; crests of glassy appearance, not breaking.

Wind felt on face; leaves rustle; vanes begin to move

3

7-10

8-12

3.4-5.4

12-19

Gentle Breeze

Gentle Breeze

Large wavelets; crests begin to break; scattered whitecaps

Leaves, small twigs in constant motion; light flags extended.

4

11-16

13-18

5.5-7.9

20-28

Moderate Breeze

Moderate Breeze

Small waves, becoming longer; numerous whitecaps.

Dust, leaves, and loose paper raised up; small branches move.

5

17-21

19-24

8.0-10.7

29-38

Fresh Breeze

Fresh Breeze

Moderate waves, taking longer form; many whitecaps; some spray.

Small trees in leaf begin to sway

6

22-27

25-31

10.8-13.8

39-49

Strong Breeze

Strong Breeze

Larger waves forming; whitecaps everywhere; more spray.

Larger branches of trees in motion; whistling heard in wires.

7

28-33

32-38

13.9-17.1

50-61

Moderate Gale

Near Gale

Sea heaps up; white foam from breaking waves begins to be blown in streaks.

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

8

34-40

39-46

17.2-20.7

62-74

Fresh Gale

Gale

Moderately high waves of greater length; edges of crests begin to break into spindrift; foam is blown in well marked streaks.

Twigs and small branches broken off trees; progress generally impeded.

9

41-47

47-54

20.8-24.4

75-88

Strong Gale

Strong Gale

High waves; sea begins to roll; dense streaks of foam; spray may reduce visibility.

Slight structural damage occurs; slate blown from roofs.

10

48-55

55-63

24.5-28.4

89-102

Whole Gale

Storm

Very high waves with overhanging crests; sea takes white appearance as foam is blown in very dense streaks; rolling is heavy and visibility reduced.

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

11

56-63

64-72

28.5-32.6

103-117

Storm

Violent Storm

Exceptionally high waves; sea covered with white foam patches; visibility still more reduced

Very rarely experienced on land; usually accompanied by widespread damage.

12
13
14
15
16
17

64-71
72-80
81-89
90-99
100-108
109-118

73-82
83-92
93-103
104-114
115-125
126-136

32.7-36.9
37.0-41.4
41.5-46.1
46.2-50.9
51.0-56.0
56.1-61.2

118-133
134-149
150-166
167-183
184-201
202-220

Hurricane

Hurricane

air filled with foam; sea completely white with driving spray; visibility greatly reduced.

Very rarely experienced on land; usually accompanied by widespread damage.