The Beaufort Scale

0 Calm

Smoke rises vertically

0 - 0.2 m/s: <1 knot

1 Light air

Smoke follows wind; wind vanes don't work

0.3 - 1.5 m/s: 1-3 knots

2 Light breeze

Leaves rustle; wind felt on face

1.6 - 3.3 m/s: 4-6 knots

3 Gentle breeze

Leaves and twigs in constant motion

3.4 - 5.4 m/s

7 - 10 knots

4 Moderate breeze

Raises dust and loose paper; small branches are moved

5.5 - 7.9 m/s

11 - 16 knots

5 Fresh breeze

Small leafy trees begin to sway; inland waters form crested wavelets

8 - 10.7 m/s

17 - 21 knots

6 Strong breeze

Large branches in motion

10.8 - 13.8 m/s

22 - 27 knots

7 Near gale

Whole trees in motion and some difficulty walking into the wind

13.9 - 17.1 m/s

28 - 33 knots

8 Gale

Twigs break off trees; difficulty walking

17.2 - 20.7 m/s

34 - 40 knots

9 Strong gale

Structural damage can occur

20.8 - 24.4 m/s

41 - 47 knots

10 Storm

Trees uprooted; severe structural damage may occur

24.5 - 28.4 m/s

48 - 50 knots

11 Violent storm

Rare; widespread damage

28.5 - 32.6 m/s

56 - 63 knots

12 Hurricane

>32.7 m/s

>64 knots