Beaufort wind scales

The best known scale for wind speed is that of Sir Francis Beaufort (1774–1857), a captain in the British Admiralty who drew up the first version in 1806 for his own use.

Ordered lists of wind names have been made for millenia (everyone knows a hurricane is stronger than a breeze, for example). Quantifying wind velocity was a later development.

portrait of Smeaton


One of the first to do so was the English engineer John Smeaton, who was interested in windmills¹ and built a device for measuring the effectiveness of windmill sails at different wind velocities. His wind scale ran from 1 to 8, describing each force by what he observed at a particular windmill, the Austhorpe Mill near his home. For example, number 2, Breeze, was “Sufficient to move the branches of trees, and Mill from 6 to 9 turns” per minute, while at number 5, Very Fresh, “Wind growing noisy, and considerable agitation of Trees, Mill 18 [turns per minute] to ¾ Cloth.”

Smeaton's scale caught the attention of the Hydrographer to the British Admiralty, Alexander Dalrymple. The Hydrographer was the person in charge of gathering data and issuing charts, and a convenient, consistent way of noting wind speed would be invaluable to the navy. Dalrymple changed the scale to 0 to 12, from Smeaton's 1 to 8, and changed the wind names to those usually used in ships' logs. And he brought his scale to the attention of Captain Beaufort, who had distinguished himself by producing meticulous records.

The genius of Beaufort's addition to the scale was that he defined each name and number by a description of the maximum amount of sail a man-of-war could carry under those wind conditions.

Force Name Description
0 Calm  
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, etc.
6 Strong breeze Single-reefed top-sails and top-gallant sails
7 Moderate gale Double-reefed top-sails, jib, etc.
8 Fresh gale Triple-reefed topsails, etc.
9 Strong gale Close-reefed top-sails and courses
10 Whole gale Or that which she could scarcely bear close-reefed main-topsail and reefed foresail.
11 Storm Or that which would reduce her to storm stay-sails.
12 Hurricane Or that which no canvas could withstand.

Notice that this scale depends on observation of a ship of a particular class sailing into the wind (“clean full”), and. for force numbers 5 through 9, on such a ship being in pursuit of an enemy vessel.³ This specificity was not much of a problem. Men-of-war were fairly standardized; any sailor familiar with them (and most were) could observe sails and assign a Beaufort number, and conversely, given a Beaufort force number, a sailor could picture wind conditions. Blair Kinsman suggests that one value of the scale to the Admiralty was that it facilitated courts-martial of captains who failed to pursue with all possible vigor.

In 1829 Beaufort was promoted to Hydrographer. According to Scott Huler, the first official use of the Beaufort scale occurred in 1831 when Beaufort directed it be used on the second voyage of the Beagle, the expedition that took Charles Darwin to the Galapagos (Beaufort had recommended him for the job).

On 28 December 1838, the Admiralty formally adopted Beaufort's scale for “all Her Majesty's Ships and Vessels of War.”

In August 1853, representatives of ten nations met in Brussels (the First International Meteorological Conference). One of their goals was to agree upon a standard format for the weather observations in ships' logbooks; the scale they adopted for the wind was Beaufort's. In 1862, the British Board of Trade adopted the scale for commercial vessels. When the International Meteorological Organization was formed (Vienna, 1873), it continued its predecessor's use of the Beaufort scale.

Beaufort wind scale on land

In the last quarter of the 19th century numerous investigations were made with the goal of assigning a range of wind speeds to each of Beaufort's numbers. The British Meteorological Office was active in this work and in 1906 published a report with wind speed ranges. This report also introduced descriptions of what would be observed on land at each Beaufort number. Huler has made a fairly convincing case that the principal author of the Land Criteria was the “North Shields observer,” one George Clark, head clerk at the North Shields Post Office. 

Wind speed
British description & WMO (1964) Meteorological Office, 1906
knots km/hr miles/hr Land criteria Coastal
0 <1 <1 <1 Light Calm Smoke rises vertically. Calm
1 1-3 1-5 1–3 Light Light air Direction of wind shown by smoke but not by wind vanes. Fishing smack just has steerage way.
2 4-6 6-11 4–7 Light Light
Wind felt on face; leaves rustle; ordinary vane moved by wind. Wind fills the sails of smacks which then travel about 1-2 knots.
3 7-10 12-19 8–12 Gentle Gentle
Leaves and small twigs in constant motion; wind extends light flag. Smacks begin to careen and travel about 3-4 knots.
4 11-16 20-28 13–18 Moderate Moderate
Raises dust and loose paper; small branches are moved. Good working breeze, smacks carry all canvas with good list.
5 17-21 29-38 19–24 Fresh Fresh
Small trees in leaf begin to sway; wavelets form on inland waters. Smacks shorten sail.
6 22-27 39-49 25–31 Strong Strong
Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty. Smacks have double reef in mainsail; care required when fishing.
7 28-33 50-61 32–38 Strong Near
Whole trees in motion; inconvenience felt when walking against the wind; umbrellas discarded in exposed places. Smacks remain in harbor and those at sea lie to.
8 34-40 62-74 39–46 Gale Gale Breaks twigs off trees; generally impedes progress All smacks make for harbor, if near.
9 41-47 75-88 47–54 Gale Strong
Slight structural damage occurs (chimney-pots and slates removed).  
10 48-55 89-102 55–63 Whole
Storm Seldom experienced inland; trees uprooted; considerable structural damage occurs.  
11 56-63 103-117 64–72 Whole
Very rarely experienced; accompanied by widespread damage.  
12 64 >118 73–82 Hurricane Hurricane [Countryside is devastated.]  
13     83–92        
14     93–103        
15     104–114        
16     115–125        
17     126–136        

Wind speed changes with height. In June, 1939 the International Meteorological Committee adopted a correlation with wind speeds measured at a height of 6 meters. Great Britain and the United States, however, had already standardized on measuring the wind speed at 11 meters above ground level, which is shown in column 2 below, in miles per hour.

Beaufort wind scale for the open sea

The replacement of sailing vessels by steam- and petroleum-powered engines made Beaufort's descriptions of sails obsolete. Instead of observing sails, sailors turned to observing the sea itself: waves, spray, froth, white caps, and so forth. Here it is necessary to distinguish between what sailors call the "sea" and swells. Swells are disturbances of the sea surface due to wind that blew many miles away, sometimes thousands of miles away. Swells have rounded crests. "Sea" is the effect of local wind.

In 1927 P. Petersen, a German sea captain, published a scale5 from 0 to 12 for the state-of-the-sea. In this he drew upon earlier shipboard measurements6 with anemometers. Today's state-of-the-sea descriptions remain largely translations from Petersen's German, and the scale is sometimes called the Petersen state-of-the-sea scale. The scale, however, remains Beaufort's, in the sense that the numbers and correlated wind speeds remain the same.

A version currently used by mariners is shown below. Please refer to the warnings following the table.

Column 2 is the range of wind speeds in knots, measured at a height of 33 feet above sea level.

Column 5 is the probable height of waves in feet in the open sea, remote from land. In enclosed waters, or when near land with an offshore wind, wave heights will be smaller and the waves steeper.

Column 6 is the probable maximum wave height in feet in the open sea (the caveats for column 5 apply here as well)

Sea Criteria (5) (6)
0 <1 Calm Sea like a mirror.
1 1–3 Light air Ripples with the appearance of scales are formed but without foam crests. ¼
2 4–6 Light breeze Small wavelets, still short but more pronounced. Crests have a glassy appearance and do not break. ½ 1
3 7–10 Gentle breeze Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses. 2 3
4 11–16 Moderate breeze Small waves, becoming longer; fairly frequent horses. 5
5 17–21 Fresh breeze Moderate waves, taking a more pronounced long form; many white horses are formed. (Chance of some spray.) 6
6 22–27 Strong breeze Large waves begin to form; the white foam crests are more extensive everywhere. (Probably some spray.) 13
7 28–33 Near gale Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind. 13½ 19
8 34–40 Gale Moderately high waves of greater length; edges of crests begin to break into spindrift. The foam is blown in well-marked streaks along the direction of the wind. 18 25
9 41–47 Strong gale High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble, and roll over. Spray may affect visibility. 23 32
10 48–55 Storm Very high waves with long overhanging crests. The resulting foam in great patches is blown in dense white streaks along the direction of the wind. On the whole the surface of the sea takes a white appearance. The tumbling of the sea becomes heavy and shocklike. Visibility affected. 29 41
11 56–63 Violent storm Exceptionally high waves. (Small and medium-sized ships might be for a time lost to view behind the waves.) The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibility affected. 37 52
12 64+ Hurricane The air is filled with foam and spray. Sea completely white with driving spray; visibility very seriously affected. 45


WARNING: For a given wind force, sea conditions can be more dangerous near land than in the open sea. In many tidal waters wave heights are liable to increase considerably in a matter of minutes.

In presenting a very similar table, the World Meterological Organization warns: “This table is only intended as a guide to show roughly what may be expected in the open sea, remote from land. It should never be used in the reverse way, i.e., for logging or reporting the state of the sea.7

1. John Smeaton.
Experimental Enquiry concerning the Natural Powers of Wind and Water to Turn Mills and Other Machines Depending on a Circular Motion. And An experimental examination of the quantity and proportion of mechanic power necessary to be employed in giving different degrees of velocity to heavy bodies from a state of rest. Also new fundamental experiments upon the collision of bodies. With five plates of machines.
London: Printed for I. and J. Taylor, 1794.

The first edition was published in 1760. Smeaton also included a table relating wind names to velocities in miles per hour and feet per second,and force on a foot-square board. Smeaton attributed the table to his friend Thomas Rouse, an amateur scientist.
      Austhorpe Mill, near Leeds, "was situated in Austhorpe Lane, at the top of what was known as Appleyard's Hill. A brick-built tower, it is remembered as just a ruined shell in 1928. The site is now the school playground of Austhorpe Primary School." (, accessed 17 Sept 2006)

2. Alexander Dalrymple.
Practical Navigation.
Never published. Two printer's proofs exist.

3. This paragraph is greatly indebted to two articles by Blair Kinsman.
Historical Notes on the Original Beaufort Scale.
The Marine Observer, vol. 39, pages 116-124. (1969)

Another article by Professor Kinsman covers much of the same ground in a more popular style: Who Put the Wind Speeds in Admiral Beaufort's Force Scale? Oceans, vol. 2 no. 2. He is also the author of the following, which we have not seen.

An exploration of the origin and persistence of the Beaufort wind force scale.
Technical Report, Chesapeake Bay Institute #39.
Annapolis: Chesapeake Bay Institute, 1968.

4. Sir William Napier Shaw and Sir George Clarke Simpson.
The Beaufort Scale of Wind-Force. Report of the Director of the Meteorological Office (W. N. Shaw) upon an inquiry into the relation between the estimates of wind-force according to Admiral Beaufort's scale and the velocities recorded by anemometers belonging to the Office, with a report upon certain points in connection with the inquiry by G. C. Simpson ... and notes by Sir G. H. Darwin...W. H. Dines and Commander Campbell Mepworth.
Official Publication No. 180.
London: The Meteorological Office, 1906.

5. P. Petersen.
Zur Bestimmung der Windstärke auf See. Für Segler, Dampfer und Luftfahrzeige.
Annalen der Hydrographie und Maritimen Meteorologie. March 1927, pages 69-72.

6. Prager.
Annalen der Hydrographie und Maritimen Meteorologie. 1905, pages 1-.

7. World Meteorological Organization.
Manual on Codes. International Codes. Vol. I.1 (Annex II to WMO Technical Regulations).
2011 edition, page A-379.


Nicholas Courtney.
Gale Force 10: The Life and Legacy of Admiral Sir Francis Beaufort.
Headline, 2002.

The most recent biography.

Scott Huler.
Defining the Wind. The Beaufort Scale, and How a Nineteenth-Century Admiral Turned Science into Poetry.
New York: Crown, 2004.

A writer with a passionate interest in Beaufort's scale details his research into its origins. Includes an extensive bibliography.


A number of maritime nations issue illustrated state-of-the-sea guides, such as:

State of Sea Booklet.
Bracknell, England: National Meteorological Library.

U.S. Dept. of Commerce. National Oceanic and Atmospheric Administration.
Guide to Sea State, Wind and Clouds.
Washington (?). No date or publication information in the publication, but circa 1995. SuDoc Number is C55.8:SE 1

W. T. R. Allen.
Wind and sea: State of sea photographs for the Beaufort wind scale.
Environment Canada, Atmospheric Environment Service, 1983.


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