Beaufort Wind Scale
The best known scale for wind speed is that of Sir Francis Beaufort (1774–1857), an admiral in the British navy who drew up the first version in 1806. The Beaufort scale was adopted by the admiralty in 1838 and by the International Meteorological Committee in 1874. Beaufort’s original scale (from 1 to 12) was made for use in the open sea and was based upon the amount of sail a man-of-war could carry (Force 12 was a wind “no canvas could withstand”). With the passing of military sail, later revisions focused on other phenomena observable in the open sea and added correlated wind speeds.
By studding this scale and observing water, you can estimate the winds speed with great accuracy.
| Beaufort Number
or Force |
Wind Speed | Description | Effects Land / Sea | ||
| mph | km/hr | knots | |||
| 0 | <1 | <1 | <1 | Calm | Still, calm air, smoke will rise vertically.
Water is mirror-like. |
| 1 | 1-3
mph |
1-5
kph |
1-3
knots |
Light Air | Rising smoke drifts, wind vane is inactive.
Small ripples appear on water surface. |
| 2 | 4-7
mph |
6-11
kph |
4-6
knots |
Light Breeze | Leaves rustle, can feel wind on your face, wind vanes begin to move.
Small wavelets develop, crests are glassy. |
| 3 | 8-12
mph |
12-19
kph |
7-10
knots |
Gentle Breeze | Leaves and small twigs move, light weight flags extend.
Large wavelets, crests start to break, some whitecaps. |
| 4 | 13-18
mph |
20-28
kph |
11-16
knots |
Moderate Breeze | Small branches move, raises dust, leaves and paper.
Small waves develop, becoming longer, whitecaps. |
| 5 | 19-24
mph |
29-38
kph |
17-21
knots |
Fresh Breeze | Small trees sway.
White crested wavelets (whitecaps) form, some spray. |
| 6 | 25-31
mph |
39-49
kph |
22-27
knots |
Strong Breeze | Large tree branches move, telephone wires begin to “whistle”, umbrellas are difficult to keep under control.
Larger waves form, whitecaps prevalent, spray. |
| 7 | 32-38
mph |
50-61
kph |
28-33
knots |
Moderate or Near Gale | Large trees sway, becoming difficult to walk.
Larger waves develop, white foam from breaking waves begins to be blown. |
| 8 | 39-46
mph |
62-74
kph |
34-40
knots |
Gale or Fresh Gale | Twigs and small branches are broken from trees, walking is difficult.
Moderately large waves with blown foam. |
| 9 | 47-54
mph |
75-88
kph |
41-47
knots |
Strong Gale | Slight damage occurs to buildings, shingles are blown off of roofs.
High waves (6 meters), rolling seas, dense foam, Blowing spray reduces visibility. |
| 10 | 55-63
mph |
89-102
kph |
48-55
knots |
Whole Gale or Storm | Trees are broken or uprooted, building damage is considerable.
Large waves (6-9 meters), overhanging crests, sea becomes white with foam, heavy rolling, reduced visibility. |
| 11 | 64-72
mph |
103-117
kph |
56-63
knots |
Violent Storm | Extensive widespread damage.
Large waves (9-14 meters), white foam, visibility further reduced. |
| 12 | 73+
mph |
118+
kph |
64+
knots |
Hurricane | Extreme destruction, devastation.
Large waves over 14 meters, air filled with foam, sea white with foam and driving spray, little visibility. |