Beaufort wind force scale

The Beaufort scale, which is used in Met Office marine forecasts, is an empirical measure for describing wind intensity based on observed sea conditions.

Specifications and equivalent speeds
Beaufort wind scale

Mean Wind Speed

Limits of wind speed


Wind descriptive terms

Probable wave height in metres*

Probable maximum wave height in metres*

Seastate
Sea descriptive terms
Knotsms-1Knotsms-1

0

0

0

<1

<1

Calm

-

-

0

Calm (glassy)

1

2

1

1-3

1-2

Light air

0.1

0.1

1

Calm (rippled)

2

5

3

4-6

2-3

Light breeze

0.2

0.3

2

Smooth (wavelets)

3

9

5

7-10

4-5

Gentle breeze

0.6

1.0

3

Slight

4

13

7

11-16

6-8

Moderate breeze

1.0

1.5

3-4

Slight - Moderate

5

19

10

17-21

9-11

Fresh breeze

2.0

2.5

4

Moderate

6

24

12

22-27

11-14

Strong breeze

3.0

4.0

5

Rough

7

30

15

28-33

14-17

Near gale

4.0

5.5

5-6

Rough-Very rough

8

37

19

34-40

17-21

Gale

5.5

7.5

6-7

Very rough - High

9

44

23

41-47

21-24

Strong gale*

7.0

10.0

7

High

10

52

27

48-55

25-28

Storm

9.0

12.5

8

Very High

11

60

31

56-63

29-32

Violent storm

11.5

16.0

8

Very High

12

-

64+

33+

Hurricane

14+

-

9

Phenomenal

*

  1. These values refer to well-developed wind waves of the open sea.
  2. The lag effect between the wind getting up and the sea increasing should be borne in mind.
  3. The official term is Strong gale, however, the Met Office uses the descriptive term Severe gale

To convert knots to mph multiply by 1.15, for m/s multiply by 0.514.

Last updated: 1 December 2014