The Modern
Beaufort Wind Force Scale

(Without Hurricane or Typhoon Extensions 13-17)

Wave heights in the scale are for conditions in the open ocean, not along the shore.

Beaufort number Wind speed Description Wave height Sea conditions Land conditions
km/h mph knots m ft
0 <1 <1 <1 Calm 0 0 Flat. Calm. Smoke rises vertically.
1 1-5 1-3 1-2 Light Air 0.1 0.33 Ripples without crests. Wind motion visible in smoke.
2 6-11 3-7 3-6 Light Breeze 0.2 0.66 Small wavelets. Crests of glassy appearance, not breaking Wind felt on exposed skin. Leaves rustle.
3 12-19 8-12 7-10 Gentle Breeze 0.6 2 Large wavelets. Crests begin to break; scattered whitecaps Leaves and smaller twigs in constant motion.
4 20-28 13-17 11-15 Moderate Breeze 1 3.3 Small waves with abundent whitecaps. Dust and loose paper raised. Small branches begin to move.
5 29-38 18-24 16-20 Fresh Breeze 2 6.6 Moderate (1.2 m) longer waves. Some foam and spray. Branches of a moderate size move. Small trees begin to sway.
6 39-49 25-30 21-26 Strong Breeze 3 9.9 Large waves with foam crests and some spray. Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult. Empty plastic garbage cans tip over.
7 50-61 31-38 27-33 High wind, Moderate Gale 4 13.1 Sea heaps up and foam begins to be blown in streaks in wind direction. Whole trees in motion. Effort needed to walk against the wind. Swaying of skyscrapers may be felt, especially by people on upper floors.
8 62-74 39-46 34-40 Fresh Gale 5.5 18 Moderately high waves with breaking crests forming spindrift. Streaks of foam. Twigs broken from trees. Cars veer on road.
9 75-88 47-54 41-47 Strong Gale 7 23 High waves (6-7 m) with dense foam. Wave crests start to roll over. Considerable spray. Larger branches break off trees, and some small trees blow over. Construction/temporary signs and barricades blow over. Damage to circus tents and canopies.
10 89-102 55-63 48-55 Whole Gale Storm 9 29.5 Very high waves. Large patches of foam from wave crests give the sea a white appearance. Considerable tumbling of waves with heavy impact. Large amounts of airborne spray reduce visibility. Trees are broken off or uprooted, saplings bent and deformed, poorly attached asphalt shingles and shingles in poor condition peel off roofs.
11 103-117 64-72 56-63 Violent storm 11.5 37.7 Exceptionally high waves. Very large patches of foam, driven before the wind, cover much of the sea surface. Very large amounts of airborne spray severely reduce visibility. Widespread vegetation damage. More damage to most roofing surfaces, asphalt tiles that have curled up and/or fractured due to age may break away completely.
12 ≥118 ≥73 ≥64 Hurricane-force ≥14 ≥46 Huge waves. Sea is completely white with foam and spray. Air is filled with driving spray, greatly reducing visibility. Considerable and widespread damage to vegetation, a few windows broken, structural damage to mobile homes and poorly constructed sheds and barns. Debris may be hurled about.

In the United States, winds of Beaufort 6 or 7 result in the issuance of a small craft advisory, with force 8 or 9 winds bringing about a gale warning, 10 or 11 a storm warning (or "tropical storm warning" for 8 to 11 if related to a tropical cyclone), and anything to 12 a hurricane warning.

In the Indian Ocean and South China Sea, this scale is extended by the addition of Numbers 13 through 17 because of the frequency of extremely forceful Typhoons in those areas.

Wind speed can be approximated using the Beaufort Force Scale. Originally, the Beaufort Scale was developed to provide a scale based on visual observations of the sea surface, you can get a very rough equation of wind speed by subtracting 1 from the number of the Beaufort Force and multiplying that by 5. The resultant number will be a rough approximation of wind speed in knots. (i.e.: Force 8 is about 35 knots +/- ((8-1) x 5 = 35).

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