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| The beaufort wind scale |
| One of the first scales to estimate wind speeds and the effects was
created by Britain's Admiral Sir Francis Beaufort (1774-1857). He
developed the scale in 1805 to help sailors estimate the winds via
visual observations. The scale starts with 0 and goes to a force of 12.
The Beaufort scale is still used today to estimate wind strengths. |
| Windspeed conversions |
Here you can convert between units. Type a number into a textbox below.
Please note that Beaufort-values are between 0 and 12. |
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| Beaufort-values corresponds to windspeed intervals. If a number is entered in the
Beaufort-box, other boxes will display appropriate median values for that Beaufort-number,
approximated to the nearest integer. If a number is entered in other boxes, the
Beaufort-box will display the approximated Beaufort-value. This approximation
inevitable leads to a slight inaccuracy in the calculations. The figure on the
right loosely shows the relationship between m/s and a few Beaufort-values. |
The prerequisites of the calculations above are:
 | The equation: W = 0,836B3/2 where W is windspeed in m/s and B
is value on the Beaufort-scale. |
| 1 m/s = 3,6 km/h = 1,944 knots = 2,237 miles per hour |
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Below is a detailed table with comparison between Beaufort-values,
average windspeed and the median for the average windspeed in m/s, km/h, knots and mph |
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| Windspeed classification |
| To ease the understanding of the m/s measurement, the following table can be used. |
Windspeed in m/s |
Description |
| <5 |
Very slow wind |
| 5-10 |
Rather slow wind |
| 10-20 |
Considerable wind, may lead to difficulties |
| 20-30 |
Very windy, caution is advised |
| >30 |
Extreme wind, dangerous |
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| Comparison with Beaufort-values |
| Windforce* |
Average windspeed** |
Median of av. windspeed |
| Beaufort |
Name |
m/s |
km/h |
knots |
miles/h |
m/s |
km/h |
knots |
miles/h |
| 0 |
Calm |
0-0,2 |
< 1 |
< 1 |
<1 |
0,0 |
0,0 |
0,0 |
0,0 |
| 1 |
Light air |
0,3-1,5 |
1-5 |
1-3 |
1-3 |
0,8 |
3,0 |
1,6 |
1,9 |
| 2 |
Light breeze |
1,6-3,3 |
6-11 |
4-6 |
4-7 |
2,4 |
8,5 |
4,6 |
5,3 |
| 3 |
Gentle breeze |
3,4-5,4 |
12-19 |
7-10 |
8-11 |
4,3 |
15,6 |
8,4 |
9,7 |
| 4 |
Mod. breeze |
5,5-7,9 |
20-28 |
11-16 |
13-18 |
6,7 |
24,1 |
13,0 |
15,0 |
| 5 |
Fresh breeze |
8,0-10,7 |
29-38 |
17-21 |
19-24 |
9,3 |
33,6 |
18,2 |
20,9 |
| 6 |
Strong breeze |
10,8-13,8 |
39-49 |
22-27 |
25-31 |
12,3 |
44,2 |
23,9 |
27,5 |
| 7 |
Near gale |
13,9-17,1 |
50-61 |
28-33 |
32-38 |
15,5 |
55,7 |
30,1 |
34,6 |
| 8 |
Gale |
17,2-20,7 |
62-74 |
34-40 |
39-46 |
18,9 |
68,1 |
36,8 |
42,3 |
| 9 |
Strong gale |
20,8-24,4 |
75-88 |
41-47 |
47-54 |
22,6 |
81,3 |
43,9 |
50,5 |
| 10 |
Storm |
24,5-28,4 |
89-102 |
48-55 |
55-63 |
26,4 |
95,2 |
51,4 |
59,1 |
| 11 |
Violent storm |
28,5-32,6 |
103-117 |
56-63 |
64-74 |
30,5 |
109,8 |
59,3 |
68,2 |
| 12 |
Hurricane |
>= 32,7 |
>= 118 |
>= 64 |
>=75 |
... |
... |
... |
... |
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| * |
Windforce measured in Beaufort-values is not an objective observation of
windspeed, but rather a subjective one, based on the impact of the wind on the
environment. |
| ** |
This empirical relation between windforce, estimated on the
Beaufort-scale, and the windspeed is based on the 10 minute average of the windspeed. In
reality, windspeeds can vary a lot in that time. As a result, windgusts can not be
measured with the Beaufort-scale. Windspeeds are now generally measured with anemometers,
which continuously record the momentary windspeed, i.e. windgusts, that can vary a great
deal from a 10 minute average windspeed an therefore bear no relations to the
Beaufort-scale. |
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