Force

Speed

Name

Conditions
at Sea

Conditions
on Land

knots

km/h

mi/h

0

< 1

< 2

< 1

Calm

Sea like a mirror.

Smoke rises vertically.

1

1-3

1-5

1-4

Light air

Ripples only.

Smoke drifts and leaves rustle.

2

4-6

6-11

5-7

Light breeze

Small wavelets (0.2 m). Crests have a glassy appearance.

Wind felt on face.

3

7-10

12-19

 8-11

Gentle breeze

Large wavelets (0.6 m), crests begin to break.

Flags extended, leaves move. 

4

11-16

20-29

12-18

Moderate breeze

Small waves (1 m), some whitecaps.

Dust and small branches move.

5

17-21

30-39

19-24

Fresh breeze

Moderate waves (1.8 m), many whitecaps.

Small trees begin to sway.

6

22-27

40-50

25-31

Strong breeze

Large waves (3 m), probably some spray.

Large branches move, wires whistle, umbrellas are difficult to control.

7

28-33

51-61

32-38

Near gale

Mounting sea (4 m) with foam blown in streaks downwind.

Whole trees in motion inconvenience in walking.

8

34-40

62-74

39-46

Gale

Moderately high waves (5.5 m), crests break into spindrift.

Difficult to walk against wind. Twigs and small branches blown off trees.

9

41-47

76-87

47-54

Strong gale

High waves (7 m), dense foam, visibility affected.

Minor structural damage may occur (shingles blown off roofs).

10

48-55

88-102

55-63

Storm

Very high waves (9 m), heavy sea roll, visibility impaired. Surface generally white.

Trees uprooted structural damage likely.

11

56-63

103-118

64-73

Violent storm 

Exceptionally high waves (11 m), visibility poor.

Widespread damage to structures.

12

64+

119+

74+

Hurricane

14 m waves, air filled with foam and spray, visibility bad.

Severe structural damage to buildings, wide spread devastation.