Beaufort Wind Scale

In 1806, Admiral Sir Francis Beaufort devised a simple scale that coastal observers could use to report the state of the sea to the Admiralty. It was officially adopted in 1838.

Beaufort Wind Speed Wind Force Sea Surface Near Coast Ships Sea Height Code
Number Knots MPH KPH
0 < 1 < 1 < 1 Calm Calm Sea like mirror Calm 0 0 Calm
1 1-3 1-3 1-5 Light air Ripples with the appearance of scales;no foam crests. Fishing smack just has steerage way. Man-of-war with all sails set will just have steerage way. 0 0 Calm
2 4-6 4-7 6-11 Light Breeze Small wavelets; crests of glassy apprearance, not breaking. Wind fills the sails of smacks which then travel at about 1-2 MPH. Man-of-war will sail at 1 to 2 knots. 1 0-0.1 Calm, rippled
3 7-10 8-12 12-19 Gentle Breeze Large wavelets; crests begin to break; scattered whitecaps. Smacks begin to careen and travel about 3-4 MPH. Man-of-war will sail at 3 to 4 knots. 2 0.1-0.5 Smooth
4 11-16 13-18 20-28 Moderate Breeze Small waves, becoming longer; numerous whitecaps. Good working breeze, smacks carry all canvas with good list. Man-of-war sails clean and full at about 5 to 6 knots. 3 0.5-1.25 Slight
5 17-21 19-24 29-38 Fresh Breeze Moderate waves, taking longer form; many whitecaps; some spray. Smacks shorten sail. Man-of-war in chase will just carry royals and courses. 4 1.25-2.5 Moderate
6 22-27 25-31 39-49 Strong Breeze Larger waves forming; whitecaps everywhere; more spray. Smacks have double reef in mainsail; care required when fishing. Man-of-war will have single reefed topsails and top-gallant sails. 5 2.5-4 Rough
7 28-33 32-38 50-61 Near Gale Sea heaps up; white foam from breaking waves begins to blow in streaks. Smacks remain in harbour and those at sea lie-to. Man-of-war will have double-reefed topsails, jib and courses. 6 4-6 Very Rough
8 34-40 39-46 62-74 Gale Moderately high waves of greater length; edges of crests begin to break into spindrift; foam is blown into wellmarked streaks. All smacks make for harbour, if near. Man-of-war will have triple-reefed topsails, jib and courses. 6 4-6 Very Rough
9 41-47 47-54 75-88 Strong Gale High waves; seas begins to roll; dense streaks of foam; spray may reduce visibility. - Man-of-war will have close-reefed topsails and courses. 6 4-6 Very Rough
10 48-55 55-63 89-102 Storm Very high waves with overhanging crests; sea takes white appearance as foam is blown in very dense streaks; rolling is heavy and visibility is reduced. - Man-of-war will scarcely bear close-reefed main-topsail and reefed foresail. 7 6-9 High
11 56-63 64-72 103-117 Violent Storm Exceptionally high waves; sea covered with white foam patches; visibility still more reduced. - Man-of-war will reduce sail to storm-staysails. 8 9-14 Very High
12 >64 >73 >118 Hurricane Air filled with foam; sea completely white with driving spray; visibility still more reduced. - Man-of-war will carry no sails. 9 14 Phenomenal