Beaufort Scale of Wind Velocity

Beaufort
Number
Wind Velocity
(knots)

Seamanís Term

Sea Condition

Typical**
Wave
Height
Feet

Typical***
Condition
Attainment
Time

0

0-1

Calm

Glassy-smooth, mirror-like  

Smooth

- -

1

2-3

Light air

Scale-like ripples

Ripples

1-10 min

2

4-6

Light breeze

Small, short wavelets with glassy crests

1/3

5-15 min

3

7-10

Gentle breeze

Large wavelets, crests begin to break, occasional form

1-2

5-20 min

4

11-16

Moderate breeze

Small waves, some whitecaps, more frequent form

2-3

15-60 min

5

17-21

Fresh breeze

Moderate longer waves, better formed, many whitecaps, much foam, some spray

3-4

15-60 min

6

22-27

Strong breeze

Large waves form, many whitecaps, foam everywhere, more spray

4-5

1/4-2 hr.

7

28-33

Moderate gale

Sea heaps up, streaks of foam spindrift begins

5-6

1/2-3 hr.

8

34-40

Fresh gale

Moderately-high long waves, crests into spindrift, well-marked streaks of foam

6-7

1/2-3 hr.

9

41-47

Strong gale

High waves, sea rolls, dense streaks, spray affects visibility

7-9

1/2-4 hr.

**

Wave height is dependent on water depth and length of time that the wind has been blowing. These are typical heights for lakes, bays and estuaries. The above conditions and wave heights should prevail after the times indicated. Don't neglect the effect of large numbers of powerboats on enclosed bodies of water in estimating wave heights.

***

These attainment times are for winds of constant or increasing intensities. For decreasing intensities, surface characteristics will have to be relied upon; for example, one-foot glassy-smooth waves still indicate BN=0 wind conditions.