The beaufort wind scale was devised by Admiral Francis Beaufort in 1805 and is still used today to easily allow an observer to judge the wind speed without the use of an instrument.
| Beaufort Number | Description | Wind Speed (Knots) | Wave Height (Metres) | Sea Conditions |
|---|---|---|---|---|
| 0 | Calm | 1 | 0 | Flat |
| 1 | Light air | 2 | 0.1 | Ripples without crests |
| 2 | Light breeze | 5 | 0.2 | Small wavelets. Crests of glassy appearance, not breaking |
| 3 | Gentle breeze | 9 | 0.6 | Large wavelets. Crests begin to break; scattered whitecaps |
| 4 | Moderate breeze | 13 | 1.0 | Small waves with breaking crests. Fairly frequent whitecaps. |
| 5 | Fresh breeze | 19 | 2.0 | Moderate waves of some length. Many whitecaps. Small amounts of spray. |
| 6 | Strong breeze | 24 | 3.0 | Long waves begin to form. White foam crests are very frequent. Some airborne spray is present. |
| 7 | Near gale | 30 | 4.0 | Sea heaps up. Some foam from breaking waves is blown into streaks along wind direction. Moderate amounts of airborne spray. |
| 8 | Gale | 37 | 5.5 | Moderately high waves with breaking crests forming spindrift. Well-marked streaks of foam are blown along wind direction. Considerable airborne spray. |
| 9 | Severe gale | 44 | 7.0 | High waves whose crests sometimes roll over. Dense foam is blown along wind direction. Large amounts of airborne spray may begin to reduce visibility. |
| 10 | Storm | 52 | 9.0 | Very high waves with overhanging crests. Large patches of foam from wave crests give the sea a white appearance. Considerable tumbling of waves with heavy impact. Large amounts of airborne spray reduce visibility. |
| 11 | Violent storm | 60 | 11.5 | Exceptionally high waves. Very large patches of foam, driven before the wind, cover much of the sea surface. Very large amounts of airborne spray severely reduce visibility. |
| 12 | Hurricane | - | 14+ | Huge waves. Sea is completely white with foam and spray. Air is filled with driving spray, greatly reducing visibility. |