The Beaufort Wind Scale is named after Sir Francis Beaufort, an admiral in the British Navy. He developed the scale in 1805 in order to estimate wind speed by noting how sails move in the wind. It turned out to be a great help and was later adapted for use on land.

Force 0
Strength: Calm
Speed: Less than 1 mile per hour (mph), less than 2 kilometers per hour (kph)
Observations: Tree leaves don't move, smoke rises vertically, sea is calm

Force 1
Strength: Light Air
Speed: 1-3 mph, 2-6 kph
Observations: Tree leaves don't move, smoke drifts slowly, sea is lightly rippled

Force 2
Strength: Slight Breeze
Speed: 4-7 mph, 7-11 kph
Observations: Tree leaves rustle, flags wave slightly, small wavelets or scale waves

Force 3
Strength: Gentle Breeze
Speed: 8-12 mph, 12-19 kph
Observations: Leaves and twigs in constant motion, small flags extended, long un-breaking waves

Force 4
Strength: Moderate Breeze
Speed: 13-18 mph, 20-29 kph
Observations: Small branches move, flags flap, waves with some whitecaps

Force 5
Strength: Fresh Breeze
Speed: 19-24 mph, 30-39 kph
Observations: Small trees sway, flags flap and ripple, moderate waves with many whitecaps

Force 6
Strength: Strong Breeze
Speed: 25-31 mph, 40-50 kph
Observations: Large branches sway, flags beat and pop, larger waves with regular whitecaps

Force 7
Strength: Moderate Gale
Speed: 32-38 mph, 51-61 kph
Observations: Whole trees sway, large waves ("heaping sea")

Force 8
Strength: Fresh Gale
Speed: 39-46 mph, 62-74
Observations: Twigs break off trees, moderately high sea with blowing foam

Force 9
Strength: Strong Gale
Speed: 47-54 mph, 75-87 kph
Observations: Branches break off trees, shingles blown from roofs, high crested waves

Force 10
Strength: Whole Gale
Speed: 55-63 mph, 88-101 kph
Observations: Some trees blown down, damage to buildings, high churning white sea

Force 11
Strength: Storm
Speed: 64-74 mph, 101 kph-119 kph
Observations: Widespread damage to trees and buildings, mountainous waves

Force 12
Strength: Hurricane
Speed: 75 mph or greater, 120 kph or greater
Observations: Severe and extensive damage

Wind Speed Estimation		Description
miles per hour	knots
less than 1	less than 1	Calm; smoke rises vertically
1 - 3	1 - 2½	Direction of wind shown by smoke drift, but not by wind vanes
4 - 7	3½ - 6	Wind felt on face; leaves rustle; ordinary vane moved by wind
8 - 12	7 - 10.4	Leaves and small twigs in constant motion; wind extends light flag
13 - 18	11.3 - 15½	Raises dust and loose paper; small branches are moved
19 - 24	16½ - 20.8	Small trees in leaf begin to sway; crested wavelets form on inland waters
25 - 31	21.7 - 26.9	Large branches in motion; whistling heard in telephone wires
32 - 38	27.8 - 33	Whole trees in motion; inconvenience felt walking against the wind
39 - 46	33.9 - 40	Breaks twigs off trees; wind generally impedes progress
47 - 54	40.8 - 47	Slight structural damage occurs
Severe begins at 58 mph	Severe begins at 50.4
55 - 63	47.8 - 54.7	Damage to chimneys and TV antennas; pushes over shallow rooted trees
64 - 74	55½ - 64.2	Rarely experienced; structural damage becomes possible
above 75 mph	above 65 kt's	Very rarely experienced
50 - 58	43½ - 50.3	Small branches or limbs broken (less than 2" diameter)
58 - 70	50.3 - 60.8	Large limbs knocked down, the size of an adult's wrist; powerlines knocked down; a few house shingles torn off.
70 - 80	60.8 - 69½	A few small trees or shrubs can be uprooted; Very large branches broken off; Barns may sustain considerable damage.
greater than 80	greater than 69½	Trees may be uprooted or snapped, power poles snapped or knocked over; large vehicles can be blown off the road. Roofs blown off homes.