Beaufort Wind Scale
Updated February 21, 2017 | Factmonster Staff 
In 1805, Sir Francis Beaufort, a rear admiral in the British navy, created the Beaufort Wind Scale to describe the wind's effect on sailing ships. He used knots to indicate the speed of the wind. This chart shows wind speed in miles per hour, based on the conversion of 1 knot = 1.15 miles per hour.
| Appearance of Wind Effects | ||||
|---|---|---|---|---|
| Number | Name | Miles Per Hour | On Water | On Land |
| 0 | Calm | less than 1 | Sea surface smooth and mirror-like | Calm, smoke rises vertically |
| 1 | Light air | 1-3 | Scaly ripples, no foam crests | Smoke drift indicates wind direction, still wind vanes |
| 2 | Light breeze | 4-7 | Small wavelets, crests glassy, no breaking | Wind felt on face, leaves rustle, vanes begin to move |
| 3 | Gentle breeze | 8-12 | Large wavelets, crests begin to break, scattered whitecaps | Leaves and small twigs constantly moving, light flags extended |
| 4 | Moderate breeze | 13-18 | Small waves 1-4 ft. becoming longer, numerous whitecaps | Dust, leaves, and loose paper lifted, small tree branches move |
| 5 | Fresh breeze | 19-24 | Moderate waves 4-8 ft taking longer form, many whitecaps, some spray | Small trees in leaf begin to sway |
| 6 | Strong breeze | 25-31 | Larger waves 8-13 ft, whitecaps common, more spray | Larger tree branches moving, whistling in wires |
| 7 | Near gale | 32-38 | Sea heaps up, waves 13-20 ft, white foam streaks off breakers | Whole trees moving, resistance felt walking against wind |
| 8 | Gale | 39-46 | Moderately high (13-20 ft) waves of greater length, edges of crests begin to break into spindrift, foam blown in streaks | Whole trees in motion, resistance felt walking against wind |
| 9 | Strong gale | 47-54 | High waves (20 ft), sea begins to roll, dense streaks of foam, spray may reduce visibility | Slight structural damage occurs, slate blows off roofs |
| 10 | Storm | 55-63 | Very high waves (20-30 ft) with overhanging crests, sea white with densely blown foam, heavy rolling, lowered visibility | Seldom experienced on land, trees broken or uprooted, "considerable structural damage" |
| 11 | Violent storm | 64-72 | Exceptionally high (30-45 ft) waves, foam patches cover sea, visibility more reduced | |
| 12 | Hurricane | 73+ | Air filled with foam, waves over 45 ft, sea completely white with driving spray, visibility greatly reduced | |
Source: NOAA’s National Weather Service Storm Prediction Center
