Weather

Modern scale

Beaufort number	Description	Wind speed	Wave height	Sea conditions	Land conditions
0	Calm	< 1 knot	0 ft	Sea like a mirror	Smoke rises vertically.
		< 1 mph	0 ft
		< 2 km/h	0 m
		< 0.5 m/s	0 m
1	Light air	1–3 knots	0–1 ft	Ripples with appearance of scales are formed, without foam crests	Direction shown by smoke drift but not by wind vanes.
		1–3 mph	0–1 ft
		2–5 km/h	0–0.3 m
		0.5–1.5 m/s	0–0.3 m
2	Light breeze	4–6 knots	1–2 ft	Small wavelets still short but more pronounced; crests have a glassy appearance but do not break	Wind felt on face; leaves rustle; wind vane moved by wind.
		4–7 mph	1–2 ft
		6–11 km/h	0.3–0.6 m
		1.6–3.3 m/s	0.3–0.6 m
3	Gentle breeze	7–10 knots	2–4 ft	Large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses	Leaves and small twigs in constant motion; light flags extended.
		8–12 mph	2–4 ft
		12–19 km/h	0.6–1.2 m
		3.4–5.5 m/s	0.6–1.2 m
4	Moderate breeze	11–16 knots	3.5–6 ft	Small waves becoming longer; fairly frequent white horses	Raises dust and loose paper; small branches moved.
		13–18 mph	3.5–6 ft
		20–28 km/h	1–2 m
		5.5–7.9 m/s	1–2 m
5	Fresh breeze	17–21 knots	6–10 ft	Moderate waves taking a more pronounced long form; many white horses are formed; chance of some spray	Small trees in leaf begin to sway; crested wavelets form on inland waters.
		19–24 mph	6–10 ft
		29–38 km/h	2–3 m
		8–10.7 m/s	2–3 m
6	Strong breeze	22–27 knots	9–13 ft	Large waves begin to form; the white foam crests are more extensive everywhere; probably some spray	Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty.
		25–31 mph	9–13 ft
		39–49 km/h	3–4 m
		10.8–13.8 m/s	3–4 m
7	High wind, moderate gale, near gale	28–33 knots	13–19 ft	Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind; spindrift begins to be seen	Whole trees in motion; inconvenience felt when walking against the wind.
		32–38 mph	13–19 ft
		50–61 km/h	4–5.5 m
		13.9–17.1 m/s	4–5.5 m
8	Gale, fresh gale	34–40 knots	18–25 ft	Moderately high waves of greater length; edges of crests break into spindrift; foam is blown in well-marked streaks along the direction of the wind	Twigs break off trees; generally impedes progress.
		39–46 mph	18–25 ft
		62–74 km/h	5.5–7.5 m
		17.2–20.7 m/s	5.5–7.5 m
9	Strong/severe gale	41–47 knots	23–32 ft	High waves; dense streaks of foam along the direction of the wind; sea begins to roll; spray affects visibility	Slight structural damage (chimney pots and slates removed).
		47–54 mph	23–32 ft
		75–88 km/h	7–10 m
		20.8–24.4 m/s	7–10 m
10	Storm,^[7] whole gale	48–55 knots	29–41 ft	Very high waves with long overhanging crests; 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; rolling of the sea becomes heavy; visibility affected	Seldom experienced inland; trees uprooted; considerable structural damage.
		55–63 mph	29–41 ft
		89–102 km/h	9–12.5 m
		24.5–28.4 m/s	9–12.5 m
11	Violent storm	56–63 knots	37–52 ft	Exceptionally high waves; small- and medium-sized ships might be for a long time lost to view behind the waves; sea is covered with long white patches of foam; everywhere the edges of the wave crests are blown into foam; visibility affected	Very rarely experienced; accompanied by widespread damage.
		64–72 mph	37–52 ft
		103–117 km/h	11.5–16 m
		28.5–32.6 m/s	11.5–16 m
12	Hurricane force ^[7]	≥ 64 knots	≥ 46 ft	The air is filled with foam and spray; sea is completely white with driving spray; visibility very seriously affected	Devastation.