Beaufort Scale

Force / Warning	Short Description	Specifications for use on Sea	Wave height* (metres)	Wind speed** at 10m above ground level
				Knots	mph	km/h
0	Calm	Smoke rises vertically		< 1	< 1	< 1
1	Light air	Ripples	0.1 (0.1)	1–3	1–3	1–5
2	Light breeze	Small wavelets	0.2 (0.3)	4–6	4–7	6–11
3	Gentle breeze	Large wavelets, crests begin to break	0.6 (1)	7–10	8–12	12–19
4	Moderate breeze	Small waves, becoming larger; fairly frequent white horses	1 (1.5)	11–16	13–18	20–28
5	Fresh breeze	Moderate waves, taking a more pronounced, longer form; many white horses are formed. Chance of some spray	2 (2.5)	17–21	19–24	29–38
6	Strong breeze	Large waves begin to form; the white foam crests are more extensive everywhere. Some spray	3 (4)	22–27	25–31	39–49
7	Near gale	Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind	4 (5.5)	28–33	32–38	50–61
8	Gale	Moderately high waves of greater length; edges of crests begin to break into spindrift. The foam is blown in well-marked streaks	5.5 (7.5)	34–40	39-46	62–74
9	Strong gale	High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over	7 (10)	41–47	47–54	75–88
10	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. The whole surface of the sea takes on a white appearance. Visibility affected	9 (12.5)	48–55	55–63	89–102
11	Violent storm	Exceptionally high waves (small and medium ships might be, for a time, lost to view behind the waves). The surface is covered with long white patches of foam lying along the direction of the wind. Everywhere, the edges of the wave crests are being blown into the froth. Visibility affected	11.5 (16)	56–63	64–72	103–117
12	Hurricane	The air is filled with foam and spray. Sea completely white with driving spray.	14 (-)	64>	73>	117>

*Wave height is only intended as a guide to what may be expected in the open sea. Bracketed figures indicate the probable maximum wave height.

**Wind speed is mean speed (i.e. the wind speed averaged over 10 minutes).

Force / Warning	Short Description	Specifications for use on Land	Mean wind speed* at 10m above ground level
			Knots	mph	km/h
0	Calm	Smoke rises vertically	< 1	< 1	< 1
1	Light air	Direction of wind shown by smoke but not by wind vanes	1–3	1–3	1–5
2	Light breeze	Wind felt on face, leaves rustle, ordinary vanes moved by wind	4–6	4–7	6–11
3	Gentle breeze	Leaves and small twigs in constant motion, wind extends light flag	7–10	8–12	12–19
4	Moderate breeze	Raises dust and loose paper, small branches are moved	11–16	13–18	20–28
5	Fresh breeze	Small trees in leaf begin to sway, crested wavelets form on inland waters	17–21	19–24	29–38
6	Strong breeze	Large branches in motion, whistling heard in electricity wires; umbrellas used with difficulty	22–27	25–31	39–49
7	Near gale	Branches, debris on roads, Loose objects displaced e.g. garden chairs/bins, Hazardous driving conditions for vulnerable road users, minor disruption to transport services (air, ferry)	28–33	32–38	50–61
8	Gale	Small branches, debris on roads, Minor damage to buildings, Damage to power lines, Power outages, Difficult to walk outdoors, Hazardous driving conditions, Delays or disruption to some transport services (air, ferry), Outdoor events cancelled	34–40	39-46	62–74
9	Strong gale	Branches break off, Several fallen trees, Damage to buildings, Damage to power lines, Widespread power outages, Dangerous conditions, possible threat to life, Transport services cancelled (air, rail, ferry, bus), Outdoor events cancelled, Some routes impassable	41–47	47–54	75–88
10	Storm	Seldom experienced inland, Several fallen trees, Damage to buildings, Damage to power lines, Widespread power outages, Danger to life, unsafe to be outdoors, Transport services cancelled (air, rail, ferry, bus), Events cancelled, Several routes impassable	48–55	55–63	89–102
11	Violent storm	Rare inland, Widespread fallen trees, Severe building damage, Widespread infrastructure damage, Widespread power outages, Danger to life, unsafe to be outdoors, Isolation of communities, Transport services cancelled (air, rail, ferry, bus), Only essential services operating, Many routes impassable	56–63	64–72	103–117
12	Hurricane	Very rare inland, Life threatening conditions, Significant and widespread infrastructure, Widespread and severe building damage, Widespread fallen trees, Isolation of communities, Disruption to essential services, Many routes impassable, Transport services cancelled (air, rail, ferry, bus)	64>	73>	117>

*Beaufort Scale wind speed are mean speeds (i.e. the wind speed averaged over 10 minutes).