Beaufort Wind Scale

In 1805, Sir Francis Beaufort, a rear admiral in the British navy, created the Beaufort Wind Scale to describe the wind's effect on sailing ships. He used knots to indicate the speed of the wind. This chart shows wind speed in miles per hour, based on the conversion of 1 knot = 1.15 miles per hour.

			Appearance of Wind Effects
Number	Name	Miles Per Hour	On Water	On Land
0	Calm	less than 1	Sea surface smooth and mirror-like	Calm, smoke rises vertically
1	Light air	1-3	Scaly ripples, no foam crests	Smoke drift indicates wind direction, still wind vanes
2	Light breeze	4-7	Small wavelets, crests glassy, no breaking	Wind felt on face, leaves rustle, vanes begin to move
3	Gentle breeze	8-12	Large wavelets, crests begin to break, scattered whitecaps	Leaves and small twigs constantly moving, light flags extended
4	Moderate breeze	13-18	Small waves 1-4 ft. becoming longer, numerous whitecaps	Dust, leaves, and loose paper lifted, small tree branches move
5	Fresh breeze	19-24	Moderate waves 4-8 ft taking longer form, many whitecaps, some spray	Small trees in leaf begin to sway
6	Strong breeze	25-31	Larger waves 8-13 ft, whitecaps common, more spray	Larger tree branches moving, whistling in wires
7	Near gale	32-38	Sea heaps up, waves 13-20 ft, white foam streaks off breakers	Whole trees moving, resistance felt walking against wind
8	Gale	39-46	Moderately high (13-20 ft) waves of greater length, edges of crests begin to break into spindrift, foam blown in streaks	Whole trees in motion, resistance felt walking against wind
9	Strong gale	47-54	High waves (20 ft), sea begins to roll, dense streaks of foam, spray may reduce visibility	Slight structural damage occurs, slate blows off roofs
10	Storm	55-63	Very high waves (20-30 ft) with overhanging crests, sea white with densely blown foam, heavy rolling, lowered visibility	Seldom experienced on land, trees broken or uprooted, "considerable structural damage"
11	Violent storm	64-72	Exceptionally high (30-45 ft) waves, foam patches cover sea, visibility more reduced
12	Hurricane	73+	Air filled with foam, waves over 45 ft, sea completely white with driving spray, visibility greatly reduced