Beaufort Scale

Courtesy Wikipedia!

Beaufort number	Description	Wind speed	Wave height	Sea conditions	Land conditions
0	Calm	< 1 km/h	0 m	Flat.	Calm. Smoke rises vertically.
		< 1 mph
		< 1 knot	0 ft
		< 0.3 m/s
1	Light air	1.1–5.5 km/h	0–0.2 m	Ripples without crests.	Smoke drift indicates wind direction. Leaves and wind vanes are stationary.
		1–3 mph
		1–3 knot	0–1 ft
		0.3–1.5 m/s
2	Light breeze	5.6–11 km/h	0.2–0.5 m	Small wavelets. Crests of glassy appearance, not breaking	Wind felt on exposed skin. Leaves rustle. Wind vanes begin to move.
		4–7 mph
		4–6 knot	1–2 ft
		1.6–3.4 m/s
3	Gentle breeze	12–19 km/h	0.5–1 m	Large wavelets. Crests begin to break; scattered whitecaps	Leaves and small twigs constantly moving, light flags extended.
		8–12 mph
		7–10 knot	2–3.5 ft
		3.5–5.4 m/s
4	Moderate breeze	20–28 km/h	1–2 m	Small waves with breaking crests. Fairly frequent whitecaps.	Dust and loose paper raised. Small branches begin to move.
		13–17 mph
		11–16 knot	3.5–6 ft
		5.5–7.9 m/s
5	Fresh breeze	29–38 km/h	2–3 m	Moderate waves of some length. Many whitecaps. Small amounts of spray.	Branches of a moderate size move. Small trees in leaf begin to sway.
		18–24 mph
		17–21 knot	6–9 ft
		8.0–10.7 m/s
6	Strong breeze	39–49 km/h	3–4 m	Long waves begin to form. White foam crests are very frequent. Some airborne spray is present.	Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult. Empty plastic bins tip over.
		25–30 mph
		22–27 knot	9–13 ft
		10.8–13.8 m/s
7	High wind, moderate gale, near gale	50–61 km/h	4–5.5 m	Sea heaps up. Some foam from breaking waves is blown into streaks along wind direction. Moderate amounts of airborne spray.	Whole trees in motion. Effort needed to walk against the wind.
		31–38 mph
		28–33 knot	13–19 ft
		13.9–17.1 m/s
8	Gale, fresh gale	62–74 km/h	5.5–7.5 m	Moderately high waves with breaking crests forming spindrift. Well-marked streaks of foam are blown along wind direction. Considerable airborne spray.	Some twigs broken from trees. Cars veer on road. Progress on foot is seriously impeded.
		39–46 mph
		34–40 knot	18–25 ft
		17.2–20.7 m/s
9	Strong gale	75–88 km/h	7–10 m	High waves whose crests sometimes roll over. Dense foam is blown along wind direction. Large amounts of airborne spray may begin to reduce visibility.	Some branches break off trees, and some small trees blow over. Construction/temporary signs and barricades blow over.
		47–54 mph
		41–47 knot	23–32 ft
		20.8–24.4 m/s
10	Storm, whole gale	89–102 km/h	9–12.5 m	Very high waves with overhanging crests. Large patches of foam from wave crests give the sea a white appearance. Considerable tumbling of waves with heavy impact. Large amounts of airborne spray reduce visibility.	Trees are broken off or uprooted, structural damage likely.
		55–63 mph
		48–55 knot	29–41 ft
		24.5–28.4 m/s
11	Violent storm	103–117 km/h	11.5–16 m	Exceptionally high waves. Very large patches of foam, driven before the wind, cover much of the sea surface. Very large amounts of airborne spray severely reduce visibility.	Widespread vegetation and structural damage likely.
		64–73 mph
		56–63 knot	37–52 ft
		28.5–32.6 m/s
12	Hurricane force	≥ 118 km/h	≥ 14 m	Huge waves. Sea is completely white with foam and spray. Air is filled with driving spray, greatly reducing visibility.	Severe widespread damage to vegetation and structures. Debris and unsecured objects are hurled about.