The Beaufort Wind Scale
One of the first scales to estimate wind speeds and the effects was created by Britain's Admiral Sir Francis Beaufort (1774-1857). He developed the scale in 1805 to help sailors estimate the winds via visual observations. The scale starts with 0 and goes to a force of 12.
The Beaufort scale is still used today to estimate wind strengths.
The Beaufort scale was long in use as a system for estimating wind speeds and was later extended to include descriptions of effects on land features as well. Today the accepted international practice is to report wind speed in knots (1 knot equals about 1.85 km, or 1.15 mi, per hour).
The Beaufort scale is divided into a series of values, from 0 for calm winds to 12 and above for hurricanes. Each value represents a specific range and classification of wind speeds with accompanying descriptions of the effects on surface features, as follows:
| Beaufort Number |
Beaufort Scale |
Velocity (mph) |
Velocity (knots) |
US Weather Bureau Term |
Effect on sea |
Probable mean height of waves (ft) |
Est. velocities on land |
| 0 |
Calm | Less than 1 |
Less than 1 |
Calm | Sea like a mirror |
... | Smoke rises vertically |
| 1 |
Light Air |
1-3 | 1-3 |
Light |
Ripples - no foam crest |
½ |
Smoke drifts. Wind vanes unmoved |
| 2 |
Light Breeze |
4-7 | 4-6 |
... | Small wavelets, crest have glassy appearence & do not break |
1 | Wind felt on face; leaves rustle; ordinary vane moved by wind. |
| 3 |
Gentle Breeze |
8-12 | 7-10 |
Gentle |
Large wavelets, crest begin to break. Scattered whitecaps. |
2½ |
Leaves & small twigs in constant motion; wind extends light flag. |
| 4 |
Moderate Breeze |
13-18 |
11-16 |
Moderate |
Small waves becoming longer. Frequent whitecaps. |
5 | Raises dust & loose paper, small branches are moved. |
| 5 |
Fresh Breeze |
19-24 |
17-21 |
Fresh |
Moderate waves, taking more pronounced long form; many white caps, some spray. |
10 | Small trees in leaf begin to sway. Crested wavelets form on inland waters. |
| 6 |
Storng Breeze |
25-31 |
22-27 |
Strong |
Large waves begin to form; extensive whitecaps everywhere, some spray. |
15 | Large branches in motion; umbrellas used with difficulty. |
| 7 |
Moderate Gale |
32-38 |
28-33 |
... | Sea heaps up & white foam from breaking waves begins to be blown in streaks along the direction of the wind. |
20 | Whole tree in motion; inconvenience felt in walking against the wind. |
| 8 |
Fresh Gale |
39-46 |
34-40 |
... | Moderately high waves of greater length. The foam is blown in well-marked streaks along the direction of the wind. |
25 | Breaks twigs off trees; generally impedes progress. |
| 9 |
Strong Gale |
47-54 |
41-47 |
Gale | High waves. Spray may affect visibility. Dense streaks of foam along direction of wind. Sea begins to roll. |
30 | Slight structural damage occurs. |
| 10 |
Whole Gale |
55-63 |
48-55 |
... | Very high waves. The surface of the sea takes on white appearance. The rolling of the sea becomes heavy & shocklike. Visibility is affected. |
35 | Trees uprooted; considerable structural damage occurs. |
| 11 |
Storm |
64-75 |
56-65 |
Whole Gale |
Exceptional high waves. Small & medium sized ships are lost to view for long periods |
40 | Considerable structural damage occurs. |
| 12 |
Hurricane |
Above 75 |
Above 65 |
Hurricane |
The air is filled with foam & spray. Sea completely white with driving spray; visibility very seriously affected |
45 or more |
Severe structural damage occurs. |
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