Beaufort Wind Scale

Used to measure the speed of wind, this scale is based on the reaction of common, easily recognizable objects to wind forces rather than on complicated scientific notation.

British Admiral Sir Francis Beaufort, the scale's inventor, assigned a Force Number (related to specific wind speed range) to each reaction.

Beaufort Scale
Beaufort Number Wind Speed (Knots) Description Land Signs Sea State
0 Below 1 Calm Smoke rises vertically. Leaves still. Mirror smooth.
1 1 - 3 Light Air Smoke drifts. Scaly ripples
2 4 - 6 Light Breeze Leaves rustle. Wind felt on face. Small wavelets. Crests do not break.
3 7 - 10 Gentle Breeze Light flags, leaves, and twigs move. Large wavelets. Crests may break.
4 11 - 16 Moderate breeze Small tree branches move. Small waves. White caps.
5 17 - 21 Fresh Breeze Small trees in motion. Moderate waves. Many white caps.
6 22 - 27 Strong Breeze Large branches in motion. Umbrellas difficult to use. Large waves. Foam crests. Spray.
7 28 - 33 Moderate Gale Whole trees move. Pressure, walking into the wind. White foam Breaking waves blown.
8 34 - 40 Fresh Gale Branches break from trees. Walking difficult. Moderately high waves. Some spindrift.
9 41 - 47 Strong Gale Slight structural damage occurs. Slate blown from roof. Higher waves. Dense foam. Crests topple with spray.
10 48 - 55 Whole Gale Trees broken. Structural damage occurs. Sea almost white. Violent waves.
11 56 - 63 Storm Widespread damage. Exceptionally high, violent waves. Bad visibility.
12 64+ Hurricane Massive violence and destruction. Sea white, much spray and foam. Visibility seriously affected.