Beaufort Scale

No.

Knots

mph

Description

Effects at sea

Effects on land

0

0

0mph

Calm

Sea like a mirror.

Smoke rises vertically.

1

1-3

1-3mph

Light air.

Ripples, but no foam crests.

Smoke drifts in the wind.

2

4-6

4-7mph

Light breeze.

Small wavelets.

Leaves rustle. Wind felt on face.

3

7-10

8-12mph

Gentle breeze.

Large wavelets crests, not breaking.

Small twigs in constant motion. Light flags extended.

4

11-16

13-18mph

Moderate wind.

Numerous whitecaps

Dust, leaves and loose paper raised. Small branches move

5

17-21

19-24mph

Fresh wind.

Many whitecaps, some spray.

Small trees sway.

6

22-27

25-31mph

Strong wind.

Larger waves form. Whitecaps everywhere. More spray.

Large branches move. Whistling in phone wires. Difficult to use umbrellas.

7

28-33

32-38mph

Very strong wind.

White foam from breaking waves begins to be blown in streaks.

Whole trees in motion.

8

34-40

39-46mph

Gale.

Edges of wave crests begin to break into spindrift.

Twigs break off trees. Difficult to walk.

9

41-47

47-54mph

Severe gale.

High waves. Sea begins to roll. Spray may reduce visibility.

Chimney pots and slates removed.

10

48-55

55-63mph

Storm.

Very high waves with overhanging crests. Blowing foam gives sea a white appearance.

Trees uprooted. Structural damage.

11

56-63

64-72mph

Severe storm.

Exceptionally high waves.

Widespread damage.

12

63

73mph

Hurricane force.

Air filled with foam. Sea completely white. Visibility greatly reduced.

Widespread damage. Very rarely experienced on land.