Beaufort Wind Force Scale

Sir Francis BeaufortRear-Admiral, Sir Francis Beaufort, was born in Ireland in 1774. He entered the Royal Navy at the age of 13 and was a midshipman aboard the Aquilon. By 1800 he had risen to the rank of Commander. In the summer of 1805 Beaufort was appointed to the command of the Woolwich, a 44 gun man-of-war.

In 1806 he wrote in his log book a wind force scale. The scale was simple and very similar to one that Alexander Dalrymple had written in a book in 1789. A year later he added some criteria to the 0-12 scale that indicated how much of a ship's sails would be employed by a British man-of-war under each condition. It was not related to the speed of the wind.

Over the following years he continued to use his scale in his logs. It was finally adopted in December 1838 by the British Admiralty for use in all Royal Navy logbooks. However, as ship design and the introduction of steam power became widespread even that scale had to be modified.

In 1912 the International Commission for Weather Telegraphy sought some agreement on velocity equivalents for the Beaufort scale. A uniform set of equivalents was accepted in 1926 and revised slightly in 1946, extending the scale to 17 values (the added five values further refining the hurricane-force winds). By 1955, wind velocities in knots replaced Beaufort numbers on weather maps.

Today's Beaufort Scale including the observed land conditions...

Beaufort Wind Force Wind Criterion
Speed Descriptive term Sea Land
Average Range American British State Description Wave Height
0 0 <1 kt
<1 mph
<1 km/h
Light Calm Calm Sea like a mirror. 0 Smoke rises vertically.
1 2 kt
2 mph
3 km/h
1-3 kts
1-3 mph
1-5 km/h
Light Light air Smooth Ripples with the appearance of scales are formed, but without foam crests. ¼ ft
0.1 m
Direction shown by smoke but not by wind vanes.
2 5 kts
6 mph
9 km/h
4-6 kts
4-7 mph
6-11 km/h
Light Light breeze Smooth Small wavelets, still short but more pronounced, crests have a glassy appearance and do not break. ½-1 ft
0.2 m
Wind felt on face; leaves rustle; ordinary vane moved by wind.
3 9 kts
10 mph
16 km/h
7-10 kts
8-12 mph
12-19 km/h
Gentle Gentle breeze Slight Large wavelets. Crests begin to break. Foam of glassy appearance. 2-3 ft
0.6 m
Leaves and small twigs in constant motion; wind extends light flag.
4 13 kts
16 mph
24 km/h
11-16 kts
13-18 mph
20-28 km/h
Moderate Moderate breeze Moderate Small waves, becoming longer. 3½-5 ft
1 m
Raises dust and loose paper; small branches are moved.
5 19 kts
22 mph
34 km/h
17-21 kts
19-24 mph
29-38 km/h
Fresh Fresh breeze Rough Moderate waves, taking a more pronounced long form. (Chance of some spray). 6-8 ft
2 m
Small trees in leaf begin to sway.
6 24 kts
28 mph
44 km/h
22-27 kts
25-31 mph
39-49 km/h
Strong Strong breeze Very Rough Large waves begin to form; the white foam crests are more extensive everywhere. (Probably some spray). 9½-13 ft
3 m
Large branches in motion; umbrellas used with difficulty.
7 30 kts
35 mph
56 km/h
28-33 kts
32-38 mph
50-61 km/h
Strong Near gale High Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind. 13½-19 ft
4 m
Whole trees in motion; inconvenience felt when walking against the wind.
8 37 kts
43 mph
68 km/h
34-40 kts
39-46 mph
62-74 km/h
Gale Gale Very High Moderately high waves of greater length; edges of crests begin to break into spondrift. The foam is blown in well marked streaks along the direction of the wind. 18-28 ft
5.5 m
Breaks twigs off trees; generally impedes progress
9 44 kts
51 mph
82 km/h
41-47 kts
47-54 mph
75-88 km/h
Gale Strong Gale Very High High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility. 23-32 ft
7 m
Slight structural damage; chimney-pots and slates removed.
10 52 kts
59 mph
96 km/h
48-55 kts
55-63 mph
89-102 km/h
Whole Gale Storm Phenomenal Very high waves with long overhanging crests. The resulting foam in great patches is blown in dense white streaks along the direction of the wind. On the whole the surface of the sea takes a white appearance. Visibility affected. 29-41 ft
9 m
Trees uprooted; considerable structural damage.
11 60 kts
68 mph
110 km/h
56-63 kts
64-72 mph
103-117 km/h
Whole Gale Violent Strom Phenomenal Exceptionally high waves. (Small and medium sized ships might be for a time lost to view behind the waves.) The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibility affected. 39-46 ft
11.5 m
Widespread damage; very rarely experienced.
12 68 kts
78 mph
124 km/h
64-71 kts
72-82 mph
118-132 km/h
Hurricane n/a n/a The air is filled with foam and spray. Sea completely white with driving spray; visibility very seriously affected. >52 ft
>14 m
Countryside is devastated.
13 76 kts
88 mph
141 km/h
72-80 kts
83-92 mph
133-148 km/h
14 85 kts
98 mph
157 km/h
81-89 kts
93-103 mph
149-165 km/h
15 95 kts
109 mph
175 km/h
90-99 kts
104-114 mph
166-183 km/h
16 104 kts
120 mph
192 km/h
100-108 kts
115-125 mph
184-200 km/h
17   >108 kts
>125 mph
>200 km/h

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