Beaufort 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.

Page Updated 9/9/2018