The Beaufort Scale

The Beaufort Scale is a convenient way to describe the force of a wind. It describes winds by their speed in nautical knots or miles per hour, a short descriptive term describing its force, such as 'Light Breeze', a more detailed land or sea state description, and a convenient Beaufort Number, ranging from 0 to 12. Wind speeds are measured at 10m (33 feet) above ground level (or sea level), so they will often seem a little less at ground level.

Francis Beaufort was born in 1774 in Ireland and began his career in the Royal Navy when he was 13, eventually becoming Rear Admiral Sir Francis Beaumont, Knight Commander of the Bath, and being the Hydrographer to the Admiralty. In the summer of 1805, whilst the commander of the Woolwich, a 44 gun man-of-war, he invented his wind force scale, although the Royal Navy didn't adopt his method until1838.

Early copies of the scale contained descriptions that are now meaningless to most of us because we don't sail in wooden fighting ships, but the scale remains with updated descriptions suited to different conditions around the world. An early version of the scale is shown below.


1 Light Air Or just sufficient to give steerage way.
2 Light Breeze Or that in which a man-of-war with all sail set, and clean full would go in smooth water from. 1 to 2 knots
3 Gentle Breeze 3 to 4 knots
4 Moderate Breeze 5 to 6 knots
5 Fresh Breeze Or that to which a well-conditioned man-of-war could just carry in chase, full and by. Royals, &c.
6 Strong Breeze Single-reefed topsails and top-gal. sail
7 Moderate Gale Double reefed topsails, jib, &c.
8 Fresh Gale Treble-reefed topsails &c.
9 Strong Gale Close-reefed topsails and courses.
10 Whole Gale Or that with which she could scarcely bear close-reefed main-topsail and reefed fore-sail.
11 Storm Or that which would reduce her to storm staysails.
12 Hurricane Or that which no canvas could withstand.


The reason for having so many ways to describe the wind is that it is, of course, invisible. Unless you have a mechanical way to measure the speed of the wind, its speed can only be estimated by looking at its effects on your surroundings. The descriptive scale is liable to revision in different parts of the world. Just as 'trees uprooted' is no use at all when you are in the middle of an ocean, 'leaves and small twigs in constant motion - wind can extend a lightweight flag.' is no use when you live in a desert and don't own a flag!


Beaufort Number
Speed in knots
Speed in miles per hour
Descriptive term
Effect on Land
Effect at Sea
Less than 1
Less than 1
Smoke rises vertically.
Sea like a mirror.
1 to 3
1 to 3
Light Air
Direction of wind shown by smoke but not wind vanes.
Ripples with the appearance ofscales are formed, but withoutfoam crests.
4 to 6
4 to 7
Light Breeze
Leaves rustle, wind felt on face and wind vanes moved by wind
Small wavelets, still short,but more pronounced. Crestshave a glassy appearance anddo not break.
7 to 10
8 to 12
Gentle Breeze
Leaves and small twigs in constant motion. Wind can extend a lightweight flag.
Large wavelets. Crests beginto break. Foam of glassyappearance. Perhaps scatteredwhite horses.
11 to 16
13 to 18
Moderate Breeze
Moves small branches and will raise dust and loose paper.
Small waves, becoming larger;
fairly frequent white horses.
17 to 21
19 to 24
Fresh Breeze
Small trees in leaf will begin to sway.
Moderate waves, taking a more
pronounced long form; manywhite horses are formed.
22 to 27
25 to 31
Strong Breeze
Whistling can be heard in phone (telegraph) wires. Large branches are in motion. Umbrellas used with
Large waves begin to form; thewhite foam crests are moreextensive everywhere.Probably some spray.
28 to 33
32 to 38
Near Gale
Whole trees in motion. Inconvenience felt when walking against the wind.
Sea heaps up and white foamfrom breaking waves begins tobe blown in streaks along thedirection of the wind.
34 to 40
39 to 46
Breaks twigs off trees and progress is impeded.
Moderately high waves of greater
length; edges of crests begin tobreak into spindrift. The foam isblown in well-marked streaksalong the direction of the wind.
41 to 47
47 to 54
Strong Gale
Slight structural damage occurs. Chimney pots and roof slates are blown off.
High waves. Dense streaks offoam along the direction of thewind. Crests of waves begin totopple, tumble and roll over.Spray may affect visibility.
48 to 55
55 to 63
Trees uprooted. Considerable structural damage occurs.
Very high waves with overhanging crests. Great patches of foam blown in dense white streaks. Visibility affected.
56 to 63
64 to 72
Violent Storm
Widespread damage to buildings. Rarely experienced in Britain.
Exceptionally high waves (smaller ships may vanish from sight behind waves) and the sea is totally covered with long white patches of foam lying along the direction of the wind. Visibility seriously affected.X
64 to 71
73 to 83
Only experienced in the tropics.
Only experienced in the tropics.The air is filled with foam and spray. Sea completely white with driving spray;visibility very seriously affected.

Click this button to go back to the last paged



This site is registered with ICRAThis page conforms to triple A accessibility standards

This is the logo of NGFL A black rectangle to tidy up the edge of the page Black rectangle that is part of the bar along the bottom of the page