| Descriptive term |
Beaufort scale number |
Mean velocity
(km/hour) |
Land criterion |
Sea criterion |
| Calm |
0 |
< 2 |
Calm; smoke rises vertically. |
Sea like a mirror. |
| Light |
1 |
2 - 6 |
Direction of wind shown by smoke drift, but not by wind vanes. |
Ripples with the appearance of scales are formed but without foam crests. |
| Light |
2 |
7 - 12 |
Wind felt on face; leaves rustle; ordinary vanes moved by wind. |
Small wavelets, still short but more pronounced; crests have a glassy appearance and do not break. |
| Moderate |
3 |
13 - 19 |
Leaves and small twigs in constant motion; wind extends light flag. |
Large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses. |
| Moderate |
4 |
20 - 30 |
Raises dust and loose paper; small branches are moved. |
Small waves, becoming longer; fairly frequent white horses. |
| Fresh |
5 |
31 - 40 |
Small trees in leaf begin to sway; crested wavelets form on inland waters. |
Moderate waves, taking a more pronounced long form; many white horses are formed (chance of some spray). |
| Strong |
6 |
41 - 51 |
Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty. |
Large waves begin to form; the white foam crests are more extensive everywhere (probably some spray). |
| Strong |
7 |
52 - 62 |
Whole trees in motion; inconvenience felt when walking against the wind. |
Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind. |
| Gale |
8 |
63 - 75 |
Breaks twigs off trees; generally impedes progress. |
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. |
| Gale |
9 |
76 - 87 |
Slight structural damage occurs. |
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. |
| Storm |
10 |
88 - 103 |
Seldom experienced inland; trees uprooted; considerable structural damage occurs. |
Very high waves with long overhanging crests; the resulting foam, in great patches, is blown in dense white streaks along the direction of the wind; on the whole, the surface of the sea takes on a white appearance; the tumbling of the sea becomes heavy and shocklike; visibility affected. |
| Storm |
11 |
104 - 117 |
Very rarely experienced; accompanied by wide-spread damage. |
Exceptionally high waves (small and medium-sized ships might be for a time lost to view behind the waves); the sea is completely covered with long white patches of foam lying along the direction of the wind; everywhere the edges of the wave crests are blown into froth; visibility affected. |
| Hurricane |
12 |
>= 118 |
Very rarely experienced; accompanied by wide-spread damage. |
The air is filled with foam and spray; sea completely white with driving spray; visibility very seriously affected. |
