Beaufort scale 

Beaufort number 0 - Calm

wind speed: <1 knots (<0.3 m/s)
wave height: no waves
sea: Flat, like a mirror
land: Smoke rises vertically

Beaufort number 1 - Light air

wind speed: 1-2 knots (0.3-1.5 m/s)
wave height: 0.33ft (0.1 m)
sea: Ripples without crests.
land: Direction of wind shown by smoke drift only

Beaufort number 2 - Light breeze

wind speed: 3-6 knots (1.5-3.3 m/s)
wave height: 0.66ft (0.2 m)
sea: Small wavelets. Crests of glassy appearance, not breaking.
land: Wind felt on exposed skin. Leaves rustle.

Beaufort number 3 - Gentle breeze

wind speed: 7-10 knots (3.3-5.5 m/s)
wave height: 2ft (0.6 m)
sea: Large wavelets. Crests begin to break; scattered whitecaps.
land: Leaves and smaller twigs in constant motion.

Beaufort number 4 - Moderate breeze

wind speed: 11-15 knots (5.5-8.0 m/s)
wave height: 3.3ft (1 m)
sea: Small waves becoming longer, fairly frequent white horses.
land: Dust and loose paper raised. Small branches begin to move.

Beaufort number 5 - Fresh breeze

wind speed: 16-20 knots (8.0-10.8 m/s)
wave height: 6.6ft (2 m)
sea: Moderate waves taking more pronounced long form. Many white horses, chance of some spray.
land: Branches of a moderate size move. Small trees begin to sway.

Beaufort number 6 - Strong breeze

wind speed: 21-26 knots (10.8-13.9 m/s)
wave height: 9.9ft (3 m)
sea: Larger waves begin to form. The spray is present. White foam crests are everywhere.
land: Large branches in motion. Whistling is heard in overhead wires. Umbrella use becomes difficult. Empty plastic garbage cans tip over.

Beaufort number 7 - Near gale

wind speed: 27-33 knots (13.9-17.2 m/s)
wave height: 13.1ft (4 m)
sea: Sea heaps up, and foam begins to be blown in streaks in wind direction.
land: Whole trees in motion. The effort needed to walk against the wind. Swaying of skyscrapers may be felt, especially by people on upper floors.

Beaufort number 8 - Fresh gale

wind speed: 34-40 knots (17.2-20.7 m/s)
wave height: 18ft (5.5 m)
sea: Moderately high waves of greater length. Edges of crest begin to break into spindrift. Foam is blown in well-mark streaks along the direction of the wind.
land: Twigs broken from trees. Cars veer on the road.

Beaufort number 9 - Strong gale

wind speed: 41-47 knots (20.7-24.5 m/s)
wave height: 23ft (7 m)
sea: High waves (6-7 m) with dense foam. Wave crests start to roll over. The spray may affect visibility.
land: Larger branches break off trees and some small trees blow over. Construction/temporary signs and barricades blow over. Damage to circus tents and canopies.

Beaufort number 10 - Storm

wind speed: 48-55 knots (24.5-28.4 m/s)
wave height: 29.5ft (9 m)
sea: Very high waves. 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.
land: Trees are broken off or uprooted, saplings bent and deformed, poorly attached asphalt shingles and shingles in poor condition peel off roofs.

Beaufort number 11 - Violent storm

wind speed: 56-63 knots (28.4-32.6 m/s)
wave height: 37.7ft (11.5 m)
sea: 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.
land: Widespread vegetation damage. More damage to most roofing surfaces, asphalt tiles that have curled up and/or fractured due to age may break away completely.

Beaufort number 12 - Hurricane

wind speed: ≥64 knots (≥32.6 m/s)
wave height: ≥46ft (≥14 m)
sea: Huge waves. Sea is completely white with foam and spray. Air is filled with driving spray, greatly reducing visibility.
land: Considerable and widespread damage to vegetation, a few windows broken, structural damage to mobile homes, and poorly constructed sheds and barns. Debris may be hurled about.