BEAUFORT SCALE
Observable Effects International Description Beaufort Number Wind Speed
meters/sec
m/s
km/hour
km/h
miles/hour
mph
knots
kt
Air calm; smoke rises vertically Calm 0 < 0.5 < 1 < 1 < 1
Direction of wind shown by smoke drift but not by wind vanes Light Air 1 0.5-1.5 1-5 1-3 1-3
Wind felt on face; leaves rustle; wind vanes moved by wind Light Breeze 2 2-3 6-11 4-7 4-6
Leaves and small twigs in continual motion; wind extends light flags Gentle Breeze 3 4-5 12-19 8-12 7-10
Raises dust, loose paper; moves small branches Moderate Breeze 4 6-8 20-29 13-18 11-15
Small trees in leaf begin to sway; white crested wavelets form on inland waters Fresh Breeze 5 9-10 30-39 19-24 16-21
Large branches in motion; umbrellas used with difficulty; telephone wires "whistle" Strong Breeze 6 11-13 40-50 25-31 22-27
Whole trees in motion; inconvenience felt walking against wind Moderate or Near Gale 7 14-17 51-61 32-38 28-33
Breaks twigs off trees; wind generally impedes progress Gale or Fresh Gale 8 18-20 62-74 39-46 34-40
Slight structural damage occurs Strong Gale 9 21-24 75-87 47-54 41-47
trees uprooted; considerable structural damage occurs Whole Gale or Storm 10 25-28 88-101 55-63 48-55
Widespread damage Violent Storm 11 29-33 102-118 64-73 56-63
Devastation Hurricane 12 > 33 > 118 > 73 > 64
[ 1 mile = 1609 m ]   [ 1 nautical mile = 1852 m ]   [ 1 knot = 1 nautical mile per hour ]