The beaufort scale
a scale for measuring the strength of the wind
There are many circumstances where it is impossible to measure the wind speed precisely and yet studying its effects on the surroundings enables a useful estimate to be made. Nowhere is this more evident than at sea and in 1805 Captain Beaufort devised a simple numerical scale of wind forces in terms of the resulting state of the sea.
(if you want the wind speed in other units, common conversions are here)
| Force | Speed (knots) | Speed (mph) | Description | On Land | At Sea |
| 0 | 0 | 0 | Calm | Smoke rises vertically | Sea like a mirror |
| 1 | 1 - 3 | 1 - 3 | Light air | Smoke drifts. Wind vane still | Small ripples |
| 2 | 4 - 6 | 4 - 7 | Light breeze | Wind felt on face. Leaves rustle, vane moves | Small wavelets, glassy crests |
| 3 | 7 - 10 | 8 - 12 | Gentle breeze | Leaves and small twigs in constant motion | Large wavelets. Crests break. Glassy foam |
| 4 | 11 - 16 | 13 - 18 | Moderate breeze | Raises dust; moves small branches | Small waves but fairly frequent "white horses". |
| 5 | 17 - 21 | 19 - 24 | Fresh breeze | Small trees in leaf begin to sway | Moderate waves, more pronounced long form. Many "white horses" |
| 6 | 22 - 27 | 25 - 31 | Strong breeze | Large branches in motion | Large Waves. Extensive foam crests. Probably some spray |
| 7 | 28 - 33 | 32 - 38 | Near Gale | Whole trees in motion | Sea heaps up. White foam streaks along wind |
| 8 | 34 - 40 | 39 - 46 | Gale | Breaks twigs off trees. Impedes progress | Moderately high waves of greater length. Edges of crests begin to break into spindrift. Foam blown in well marked streaks in the wind. |
| 9 | 41 - 47 | 47 - 54 | Severe Gale | Slight structural damage possible. Tree branches may break. | High waves. Dense foam streaks along wind. Wave crests begin to topple and roll over. Spray may effect visibility. |
| 10 | 48 - 55 | 55 - 63 | Storm | Seldom experienced inland. Trees uprooted. Considerable structural damage. | Very high waves with long overhanging crests. Dense large patches of foam blown along wind. Sea surface white. Visibility reduced. |
| 11 | 56 - 63 | 64 - 72 | Violent Storm | Rarely experienced. Widespread damage. | Exceptionally high waves. Sea covered with long white patches of foam along wind. Everywhere edges of wave crests blown to froth. Visibility much reduced. |
| 12 | 64+ | 73+ | Hurricane | Widespread severe damage | Air filled with foam and spray. Sea completely white with driving spray. Visibility seriously affected. |
Conversions:
| One Knot | = 1.15078 Miles per hour |
| = 1.85200 Kilometres per hour | |
| = 0.51444 metres per second | |
| = 1.68781 feet per second | |
| One Mile per hour | = 0.86898 Knots |
| = 1.60934 Kilometres per hour | |
| = 0.44704 metres per second | |
| = 1.46667 feet per second | |
| One Kilometre per hour | = 0.53996 Knots |
| = 0.62137 Miles per hour | |
| = 0.27778 metres per second | |
| = 0.91134 feet per second | |
| One metre per second | = 1.94384 Knots |
| = 2.23694 Miles per hour | |
| = 3.60000 Kilometres per hour | |
| = 3.28084 feet per second | |
| One foot per second | = 0.59248 Knots |
| = 0.68182 Miles per hour | |
| = 1.09728 Kilometres per hour | |
| = 0.30480 metres per second |
Page updated 14/02/2012 15:20:00
Background Image from Alison Bradley