The Beaufort scale is a handy device for estimating wind speed. It was devised in 1805 by a British Admiral, Sir Francis Beaufort (1774-1857). Beaufort's intention was to create a standard method of assessing wind speed, based on sailors' descriptions of the wind's effect on the water. In 1926 the scale was modified so it could also be used on land.
The Beaufort Scale designates numbers from 0 to 17 to indicate wind speeds, as shown in the table below.
|Wind speed (mph)||Beaufort Number||Wind Effect on Land||Official Description|
|Less than 1||0||Calm; smoke rises vertically.||CALM|
|1-3||1||Wind direction is seen in direction of smoke, but is not revealed by weather vane.||LIGHT AIR|
|4-7||2||Wind can be felt on face; leaves rustle; wind vane moves.||LIGHT BREEZE|
|8-12||3||Leaves and small twigs in motion; wind extends light flag.||GENTLE|
|13-18||4||Wind raises dust and loose papers; small branches move.||MODERATE|
|19-24||5||Small trees with leaves begin to sway; crested wavelets appear on inland waters.||FRESH|
|25-31||6||Large branches move; telegraph wires whistle; umbrellas become difficult to control.||STRONG|
|32-38||7||Whole trees sway and walking into the wind becomes difficult.||NEAR GALE|
|39-46||8||Twigs break off trees; cars veer on roads.||GALE|
|47-54||9||Slight structural damage occurs (roof slates may blow away, etc.).||STRONG GALE|
|55-63||10||Trees are uprooted; considerable structural damage is caused.||STORM|
|64-72||11||Widespread damage is caused.||VIOLENT STORM|
|73 or more||12||Widespread damage is caused.||HURRICANE|
Source: Williams, Jack. The Weather Book, p. 43.