| Beaufort number |
General description |
Velocity |
Sea criterion |
Landman's criterion |
| Knots |
Km/h |
| 0 |
Calm |
1 |
1 |
Sea like a mirror |
Calm. Smoke rises vertically. |
| 1 |
Light air |
1 to 3 |
1 to 5 |
Ripples with the appearance of scales are formed but without foam crests. |
Direction of wind shown by smoke drift but not by wind vanes. |
| 2 |
Light breeze |
4 to 6 |
6 to 11 |
Small wavelets, still short but more pronounced. Crests have a glassy appearance and do not break. |
Wind felt on face. Leaves rustle. Ordinary vane moved by wind. |
| 3 |
Gentle breeze |
7 to 10 |
12 to 19 |
Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses. |
Leaves and small twigs in constant motion. Wind extends light flags. |
| 4 |
Moderate breeze |
11 to 16 |
20 to 28 |
Small waves becoming longer. Fairly frequent white horses |
Raises dust and loose paper. Small branches are moved. |
| 5 |
Fresh breeze |
17 to 21 |
29 to 38 |
Moderate waves, taking a more pronounced long form. Many white horses are formed. Chance of some spray. |
Small trees in leaf begin to sway. Crested wavelets form on inland waters. |
| 6 |
Strong breeze |
22 to 27 |
39 to 49 |
Large waves begin to form. The white foam crests are more extensive everywhere. Probably some spray. |
Large branches in motion. Whistling in telegraph wires. Umbrellas used with difficulty. |
| 7 |
Near gale |
28 to 33 |
50 to 61 |
Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind. |
Whole trees in motion. Inconvenience felt when walking against the wind. |
| 8 |
Gale |
34 to 40 |
62 to 74 |
Moderately high waves of greater length. Edges of crests begin to break into spindrift. The foam is blown in well-marked streaks along the direction of the wind. |
Breaks twigs off trees. Generally impedes progress. |
| 9 |
Strong gale |
41 to 47 |
75 to 88 |
High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility. |
Slight structural damage occurs (chimney pots and slates removed). |
| 10 |
Storm |
48 to 55 |
89 to 102 |
Very high waves with long overhanging crests. Foam in great patches is blown in dense white streaks along the direction of the wind. The surface takes on a white appearance. The tumbling of the sea becomes heavy and shock-like. Visibility affected. |
Seldom experienced inland. Trees uprooted. Considerable structural damage occurs. |
| 11 |
Violent storm |
56 to 63 |
103 to 117 |
Exceptionnally high waves. The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere edges of waves crests are blown into froth. Visibility impaired. |
| 12 |
Hurricane force |
64 and over |
118 and over |
The air is filled with foam and spray. Sea completely white with driving spray; visibility very seriously impaired. |
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