Wind speed |
Terms |
Speed in knots |
Speed in km/h |
Sea state |
0 |
Calm |
Less than 1 |
Less than 1 |
Mirror |
1 |
Very light breeze |
1 to 3 |
1 to 5 |
A few ripples |
2 |
Light breeze |
4 to 6 |
6 to 11 |
Non-breaking wavelets |
3 |
Gentle breeze |
7 to 10 |
12 to 19 |
Appearance of whitecaps |
4 |
Moderate breeze |
11 to 15 |
20 to 28 |
Small waves, many whitecaps |
5 |
Fresh breeze |
16 to 21 |
29 to 38 |
Moderate waves, whitecaps, some spray. |
6 |
Strong breeze |
22 to 27 |
39 to 49 |
White foam tips, spray. |
7 |
Near gale |
28 to 33 |
50 to 61 |
Waves beginning to break, trails of foam and a lot of spray. |
8 |
Gale |
34 to 40 |
62 to 74 |
Breakers, swirls of foam at the tip of the waves, a lot of spray. |
9 |
Strong gale |
41 to 47 |
75 to 88 |
High breakers. A lot of swirling foam. Visibiility reduced by spray. |
10 |
Storm |
48 to 55 |
89 to 102 |
Large breakers. Large sheets of foam. Visibiility reduced by spray. |
11 |
Violent storm |
56 to 63 |
103 to 117 |
Very large breakers. Very large sheets of foam. Visibility greatly reduced by spray. |
12 |
Hurricane |
equal to or greater than 64 |
equal to or greater than 118 |
Enormous breakers. The sea is completely white. Visibility substantially reduced by spray. |
This scale was thought up by the British Admiral Francis Beaufort (1774-1857) in 1805. |