Beaufort Scale

The Beaufort Scale was devised by Sir Francis Beaufort in the early 1800s as a way to gauge and describe wind speeds by observation at sea, the land descriptions being added at a later date. In the west the scale ends at force 12; where as in the far east it’s extended to force 17 to accommodate typhoon conditions.

Force Description Wind Speed kmh Wind Speed knot Wind Speed mph Land Signs Sea State
0 Calm 0 – 1.4 0 – 0.8 0 – 0.9 Smoke rises vertically Mirror Smooth
1 Light Air 1.5 – 5 0.9 – 2 1 – 3 Smoke drifts to indicate wind direction. Scaly Ripple
2 Light Breeze 5 – 11 2 – 5 4 – 7 Leaves rustle, wind
vane moves		 Small wavelets, crests do not break
3 Gentle Breeze 12 – 20 6 – 9 8 – 12 Light flag will wave,
small twigs and leaves move constantly		 Large wavelets. Crests begin to break; scattered whitecaps
4 Moderate Breeze 21 – 29 10 – 14 13 – 18 All flags extended, small branches move, dust and paper blow about Small waves with breaking crests. Fairly frequent white horses.
5 Fresh Breeze 30 – 39 15 – 20 19 – 24 Small trees begin
to sway. Branches of a moderate size move.		 Moderate waves, many white horses. Small amounts of spray.
6 Strong Breeze 40 – 50 21 – 26 25 – 31 Large branches move. Whistling heard in overhead wires. Umbrella use becomes difficult. Long waves begin to form. White foam crests are very frequent. Some airborne spray is present.
7 Near Gale 51 – 61 27 – 32 32 – 38 Walking into wind difficult, whole trees move. Sea heaps up. Some foam from breaking waves is blown into streaks along wind direction. Moderate amounts of airborne spray.
8 Gale 62 – 74 33 – 40 39 – 46 Twigs break from trees,
walking very difficult		 Moderately high waves with breaking crests forming spindrift. Well-marked streaks of foam are blown along wind direction. Considerable airborne spray.
9 Strong Gale 75 – 87 41 – 47 47 – 54 Roof and fence damage. Some branches break off trees, and some small trees blow over. High waves whose crests sometimes roll over. Dense foam is blown along wind direction. Large amounts of airborne spray may begin to reduce visibility.
10 Storm 88 – 101 48 – 54 55 – 63 Trees uprooted, structural damage. Very high waves with overhanging crests. 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.
11 Violent Storm 102 – 121 55 – 65 64 – 75 May cause widespread damage, rare inland 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.
12 Hurricane 122+ 66+ 76+ Causes devastation. Huge waves. Sea is completely white with foam and spray. Air is filled with driving spray, greatly reducing visibility.