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Convert wind speed from mph to knots or kilometeres per hour

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Beaufort Wind Scale in Miles per hour (Mph), knots and Kilometers per hour (Km/h)

 

Admiral Beaufort created the Beaufort Wind Force Scale between 1813 and 1408 when it was finnaly approved by the British Admiralty. Its purpose was to allow sailors to estimate the wind speed from looking at the sea and thus keep better records of the weather.

 

Beaufort Scale Force

Wind in MPH

Wind  in Knots

Wind  in Km/h

Description - Wave Heights—Visible Condition

Force 0

 0-1      

0-1      

0-1      

Calm;  Ht 0.0m ~ At sea no waves - glassy like appearance of sea.
On land smoke rises vertically.

Force 1

1 - 4

1 - 3

2 – 6

Light Airs Ht 0m ~ At Sea wind makes glassy ripples on water.
On land direction of wind shown by smoke but not by wind vanes

Force 2

4 - 7

4 - 6

7 – 11

Light breeze Ht 0.1m ~ At Sea smooth wavelets

On land wind felt on face; leaves rustle; ordinary wind vane moved by wind 

Force 3

8 - 12

7-10

13 - 19

Gentle breeze Ht 0.4m Slight ~  At sea slight waves no white horses.

On land eaves and small twigs in constant motion; wind extends light flag 

Force 4

13 - 18

11-16

20 – 30

Moderate breeze Ht 1m - Slight to moderate ~  At Sea waves described as with occasional white horses.

On land raises dust and loose paper; small branches are moved 

Force 5

9 - 24

17 - 21

31- 39

Fresh breeze Ht 2m Moderate ~ At sea  consistent white horses

On land small trees in leaf begin to sway; crested wavelets form on lakes.

Force 6

40 - 31

22 - 27

40 – 60

Strong breeze Ht 3m Rough

At Sea large waves start to form, more extensive white foam crests, some blown spray.

On land large branches in motion; telephone wires whistle; umbrellas unsafe

Force 7

32 - 38

28 - 33

51 – 61

Moderate (near) gale Ht 4m Rough to very rough.

At Sea waves begin to heap up and streaks begin to appear down the waves.

On land whole trees in motion; inconvenience in walking against wind 

Force 8

39 - 46

34 - 40

62 – 74

Fresh gale Ht 5.5m Very rough to high

At Sea waves get longer - crests break into spindrift and the streaks become more pronounced.

 On land breaks twigs off trees; generally impedes progress 

Force 9

47 - 54

41 - 47

75 – 88

Strong or severe gale Ht 7m High

At Sea high waves and dense streaks of foam may begin to affect visibility.

On land slight structural damage occurs; chimney pots and slates removed 

Force 10

55 - 63

48 - 55

89 -   102

Whole gale or Storm - Ht 9m Very High

At Sea very high waves with overhanging crests, lots of spray makes the sea almost white, visibility seriously affected.

On land trees uprooted; considerable structural damage occurs 

Force 11

64 - 72

56 - 63

103 – 117

Violent Storm Ht 11m Very High

At Sea exceptionally high waves and a complete coverage of long white foam patches. All crests blown into froth.

On land very  rarely experienced; accompanied by widespread damage.

12

73+

64 +

118 +

Hurricane Ht 14m plus Phenomenal

At sea the air is completely filled with driving spray, visibility extremely difficult.

On land devastation occurs.

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