The scale was devised in 1805 by the Irish hydrographer Francis Beaufort (later Rear Admiral Sir Francis Beaufort), a Royal Navy officer while serving on HMS Woolwich. Air filled with foam and spray, very poor visibility Sea covered in white foam, visibility seriously affectedĭevastation. Medium-sized ships lost to view behind waves. Very rarely experienced, accompanied by widespread damage. Seldom experienced inland trees uprooted considerable structural damage. Wave crests topple over, and spray affects visibility Slight structural damage (chimney pots and slates removed). Wave crests begin to break into spindrift Twigs break off trees, generally impedes progress. Whole trees in motion inconvenience felt when walking against the wind.

Large branches in motion whistling heard in telegraph wires umbrellas used with difficulty. Small trees in leaf begin to sway crested wavelets form on inland waters. Small waves, fairly frequent white horses

Raises dust and loose paper small branches moved. Leaves and small twigs in constant motion light flags extended. Wind felt on face leaves rustle wind vane moved by wind. Sea like a mirrorĭirection shown by smoke drift but not by wind vanes. The figure for sea state (on a scale from 0-9) is a shorthand way of describing the sea surface conditions to various users. The specifications are descriptions of likely observations on land or at sea, and the probable and maximum wave heights (in metres) are quoted for the open sea. At 2 metres, wind speed may be only 50-70% of these figures. They do not reflect the wind speeds that you would feel on the ground. The wind speeds shown in the table below and that you hear quoted in weather or news reports are always measured at 10 metres above the ground using meteorological instruments. Its full name is the Beaufort wind force scale.īelow is a table showing the Beaufort Scale with speeds in knots, miles per hour and kilometres per hour. Please note that these are mean speeds, usually averaged over 10 minutes by convention, and do not capture the speed of wind gusts.

The Beaufort Scale is an empirical measure that relates wind speed to observed conditions at sea or on land.

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