Beaufort scale
| Beaufort Number | Wind Description |
Wind Speed knots |
Wind Speed mph | Wave Height | Visual Clues |
| 0 | Calm | 0 | < 1 | 0m | Sea is like a mirror |
| 1 | Light Air | 1-3 | 1-3 | 0.1m | Ripples with the appearance of scales are formed, but without foam crests. |
| 2 | Light Breeze | 4-6 | 4-7 | 0.2 - 0.3m | Small wavelets, still short but more pronounced, crests have glassy appearance and do not break. Wind felt on face. |
| 3 | Gentle Breeze | 7-10 | 8-12 | 0.6 - 1m | Large wavelets, crests begin to break. Foam of glassy appearance. Perhaps scattered white horses (white caps). |
| 4 | Moderate Breeze | 11-16 | 13-18 | 1 - 1.5m | Small waves, becoming longer. Fairly frequent white horses (white caps). |
| 5 | Fresh Breeze | 17-21 | 19-24 | 2 - 2.5m |
Moderate waves, taking more pronounced long form. Many white horses (white caps) are formed (chance of some spray). |
| 6 | Strong Breeze | 22-27 | 25-31 | 3 - 4m | Large waves begin to form. White foam crests are more extensive everywhere (probably some spray). |
| 7 | Moderate Gale | 28-33 | 32-38 | 4 - 5.5m | Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of wind. |
| 8 | Gale | 34-40 | 39-46 | 5.5 - 7.5m | Moderately high waves of greater length. Edges of crests begin to break into the spindrift. The foam is blown in well-marked streaks along the direction of the wind |
| 9 | Strong Gale | 41-47 | 47-54 | 7 - 10m | High waves. Dense streaks of foam along direction of wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility. |
| 10 | Storm | 48-55 | 55-63 | 9 - 12.5m | Very high waves with long overhanging crests. The resulting foam, in great patches is blown in dense streaks along the direction of the wind. On the whole, the sea takes on a whitish appearance. Tumbling of the sea becomes heavy and shock-like. Visibility affected. |
| 11 | Violent Storm | 56-63 | 64-72 | 11.5 - 16m | Exceptionally high waves (small and medium-sized ships might be for 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 greatly affected. |
| 12 | Hurricane | 64+ | 73+ | 14+ m | Devastation. Foam and spray. The sea is white with lots of spray. Very poor visibility |
History of the Beaufort Scale