The Beaufort scale is a scale developed in 1805 by Britain's Admiral Sir Francis Beaufort (1774-1857). The scale was developed to help sailors estimate wind speeds via visual observations. The scale starts at 0 (no wind) and goes to a force of 12 (hurricane-force winds). The Beaufort scale is still used today to esitmate wind strengths.
| Force | Wind Speed | Description | Specifications for land and sea |
|---|---|---|---|
| 0 | 0 - 1 mph 0 - 1 knots 0 - 1 km/h |
Calm | Land: Calm; smoke rises vertically. Sea: Sea like a mirror. |
| 1 | 1 - 3 mph 1 - 3 knots 1 - 5 km/h |
Light air | Land: Direction of wind shown by smoke drift, but not by wind vanes. Sea: Ripples with the appearance of scales are formed, but without foam crests. Wave heights 0 - 1 foot / 0.1 m. |
| 2 | 4 - 7 mph 4 - 6 knots 6 - 11 km/h |
Light breeze | Land: Wind felt on face; leaves rustle; ordinary vanes moved by wind. Sea: Small wavelets, still short, but more pronounced. Crests have a glassy appearance and do not break. Wave heights 1 - 2 feet / 0.1 - 0.6 m. |
| 3 | 8 - 12 mph 7 - 10 knots 12 - 19 km/h |
Gentle breeze | Land: Leaves and small twigs in constant motion; wind extends light flag. Sea: Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses. Wave heights 1 - 2 feet / 0.1 - 0.6 m. |
| 4 | 13 - 18 mph 11 - 16 knots 20 - 29 km/h |
Moderate breeze | Land: Raises dust and loose paper; small branches are moved. Sea: Small waves, becoming larger; fairly frequent white horses. Wave heights 2 - 4 feet / 0.6 - 1 m. |
| 5 | 19 - 24 mph 17 - 21 knots 30 - 39 km/h |
Fresh breeze | Land: Small trees in leaf begin to sway; crested wavelets form on inland waters. Sea: Moderate waves, taking a more pronounced long form; many white horses are formed. Chance of some spray. Wave heights 4 - 8 feet / 1 - 2 m. |
| 6* | 25 - 31 mph 22 - 27 knots 40 - 50 km/h |
Strong breeze | Land: Large branches in motion; whistling heard in telegraph wires; umbrellas used with
difficulty. Sea: Large waves begin to form; the white foam crests are more extensive everywhere. Probably some spray. Wave heights 8 - 13 feet / 2 - 4 m. |
| 7 | 32 - 38 mph 28 - 33 knots 51 - 61 km/h |
Near gale | Land: Whole trees in motion; inconvenience felt when walking against the wind. Sea: Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind. Wave heights 13 - 20 feet / 4 - 6 m. |
| 8 | 39 - 46 mph 34 - 40 knots 62 - 74 km/h |
Gale | Land: Breaks twigs off trees; generally impedes progress. Sea: 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. Wave heights 20 - 30 feet / 6 - 9 m. |
| 9 | 47 - 54 mph 41 - 47 knots 75 - 87 km/h |
Severe gale | Land: Slight structural damage occurs (chimney-pots and slates removed). Sea: 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. Wave heights 30 - 45 feet / 9 - 14 m. |
| 10 | 55 - 63 mph 48 - 55 knots 88 - 102 km/h |
Storm | Land: Seldom experienced inland; trees uprooted; considerable structural damage
occurs. Sea: Very high waves with long over-hanging 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 on a white appearance. The 'tumbling' of the sea becomes heavy and shock-like. Visibility affected. Wave heights over 45 feet / above 14 m. |
| 11 | 64 - 72 mph 56 - 63 knots 103 - 116 km/h |
Violent storm | Land: Very rarely experienced; accompanied by wide-spread damage. Sea: Exceptionally high waves (small and medium-size 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. Wave heights over 45 feet / above 14 m. |
| 12 | 73 - 83 mph 64 - 71 knots 117 - 134 km/h |
Hurricane | Land: Very rarely experienced; extreme destruction. Sea: The air is filled with foam and spray. Sea completely white with driving spray; visibility very seriously affected. Wave hieghts over 45 feet / above 14 m. |
* Small craft advisories are usually issued when a force 6 is reached.
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