60
15. The Beaufort scale
The Beaufort scale is an empirical scale for estimating the wind speed without using measuring instruments. It works
by relating wind speed to observed conditions on sea or land, such as the movement of trees or waves on the surface
of the ocean. It was named after Sir Francis Beaufort. The wind speed on land and sea is calculated in different
ways. The anemometer displays measurements on the Beaufort scale from 0-12 using a bar graph. The table below
provides an approximate conversion of Beaufort measurements into different units.
Beaufort scale
m/s
kts
mph
km/h
ft/min
0
Calm
0 - 0.2
0 - 1
0 - 1
0 - 1
0 - 58
1
Light air
0.3 - 1.5
1 - 3
1 - 3
1 - 5
59 - 314
2
Light breeze
1.6 - 3.3
4 - 6
4 - 7
6 - 11
315 - 668
3
Gentle
breeze
3.4 - 5.4
7 - 10
8 - 12
12 - 19
669 - 1082
4
Moderate
breeze
5.5 - 7.9
11 - 16
13 - 18
20 - 28
1083 - 1574
5
Fresh breeze 8.0 - 10.7
17 - 21
19 - 24
29 - 38
1575 - 2125
6
Strong
breeze
10.8 - 13.8
22 - 27
25 - 31
39 - 49
2126 - 2735
7
Near gale
13.9 - 17.1
28 - 33
32 - 38
50 - 61
2736 - 3385
8
Gale
17.2 - 20.7
34 - 40
39 - 46
62 - 74
3386 - 4093
9
Strong gale
20.8 - 24.4
41 - 47
47 - 54
75 - 88
4094 - 4822
10
Storm
24.5 - 28.4
48 - 55
55 - 63
89 - 102
4823 - 5609
11
Violent storm 28.5 - 32.6
56 - 63
64 - 72
103 - 117
5610 - 6417
12
Hurricane
force
32.6
>63
>72
>117
>6417
