Beaufort Scale

The Beaufort Scale

This scale of wind speeds devised in 1805 by Rear Admiral (RN) Sir Francis Beaufort is still used today. The wave heights are for open water – and there’s a delay between an increase in wind and the rising sea.

 

Force                   Speed                  Wave height        Conditions

(knots)      (km/h)      (feet)                  (feet)

0                <1              <1              0                         Calm, sea like a mirror.

1                1-3             1-5             0.25                    Light air, ripples.

2                4-6             6-11           0.5 – 1                 Light breeze, small wavelets (0.2m). Crests have a glassy appearance.

3                7-10           12-19         2 – 3                    Gentle breeze, large wavelets, crests begin to break, scattered

whitecaps.

4                11-16         20-29         31⁄2 – 5                Moderate breeze, small waves, numerous whitecaps.

5                17-21         30-39         6 – 8                    Fresh breeze, moderate waves, many whitecaps, some spray.

6                22-27         40-50         91⁄2-13                Strong breeze, large waves, whitecaps everywhere, more spray.

7                28-33         51-61         131⁄2-19              Near gale, mounting sea with some foam blown in streaks.

8                34-40         62-74         18-25                  Gale, moderately high waves, crests begin to break into spindrift, foam is blown in well-marked streaks

9                41-47         76-87         23-32                  Strong gale, high waves, sea begins to roll, dense foam, spray may reduce visibility.

10              48-55         88-102       29-41                  Storm, very high waves with overhanging crests, heavy sea roll, visibility reduced. Sea looks white.

11              56-63         103-118     37-52                  Violent storm, exceptionally high waves (11m), visibility poor.

12              64+            119            45 and over        Hurricane, air filled with foam, completely white with driving spray, visibility bad.