Beaufort Scale

The Beaufort scale was devised in 1805 by Admiral Francis Beaufort to improve maritime safety. It uses visual cues from the sea and the ship that allow ordinary seamen to assess the wind speed with some degree of accuracy. Much later, Sir George Simpson, a director of the UK Meteorological Office, introduced new visual cues for land-based observations.

NB: 1 knot = 0.51477 m/s = 1.15 mph

Beaufort Range	Hourly-mean Wind Speed	Description of Wind	Visual Criteria At Sea	Visual Criteria On Land
0	< 1 kt	Calm	Sea is mirror smooth	Smoke rises vertically
1	1 - 4 kts	Light Air	Small wavelets like scales, but no foam crests	Smoke drifts, wind vanes do not turn
2	4 - 7 kts	Light Breeze	Waves are short and more pronounced	Wind felt on face, leaves rustle, wind vanes turn wind
3	7 - 11 kts	Gentle Breeze	Crests begin to break: foam is glassy, not white	Leaves and twigs move, light flags extend
4	11 - 17 kts	Moderate Breeze	Waves longer: many white horses	Raises dust and paper and moves small branches
5	17 - 22 kts	Fresh Breeze	Waves are more pronounced: white foam crests seen everywhere	Small trees in leaf begin to sway
6	22 - 28 kts	Strong Breeze	Larger waves form: foam crests more extensive	Larger branches begin to move, telephone wires whistle
7	28 - 34 kts	Near Gale	Sea heaps up: foam begins to blow in streaks	Whole trees in motion
8	34 - 41 kts	Gale	Waves increase visibly: foam is blown in dense streaks	Twigs break, progress impeded
9	41 - 48 kts	Strong Gale	Waves increase visibly: foam is blown in dense streaks	Slight structural damage, chimney pots removed
10	48 - 55 kts	Storm	High waves with long overhanging crests: great foam patches	Trees uprooted, considerable structural damage
11	55 - 63 kts	Violent Storm	Ships are hidden in troughs: air filled with spray	Widespread damage
12	> 63 kts	Hurricane	Ships are hidden in troughs: air filled with spray	Countryside devastated