Windspeed

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The Icelandic Meteorological Office now uses the SI (Systeme Internationale dŽUnites) measurement metres per second (m/s) instead of the Beaufort-scale in wind measurements. The reasons for this decision are numerous. The Beaufort-scale was never intended to provide accurate windspeed measurements, but rather an estimate based upon the impact of the wind on the environment. Also modern anemometers, used in observations, measure windgusts which can not be reported using the Beaufort-scale. Lastly, other Nordic meteorological institutes have used this system for years with satisfactory results.

Windspeed conversions

Here you can convert between units. Type a number into a textbox below and then click outside it. Please note that Beaufort-values are between 0 and 12.

Beaufort:

m/s:

km/h:

knots:

miles/h:

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:
bulletThe equation: W = 0,836B3/2 where W is windspeed in m/s and B is value on the Beaufort-scale.
bullet1 m/s = 3,6 km/h = 1,944 knots = 2,237 miles per hour

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.

Beaufort - m/s comparison

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

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 Moderate 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 ... ... ... ...
* 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.