THE BEAUFORT SCALE AT A GLANCE

The Beaufort Scale

The Beaufort Scale or Beaufort Wind Force Scale is a system for estimating wind strengths without the use of instruments, based on the effects wind has on the physical environment. The behaviour of smoke, waves, trees, etc., is rated on a 13 point scale of 0 (calm) to 12 (hurricane). The scale was devised in 1805 by the British naval Commander, later Admiral, Sir Francis Beaufort (1774-1875). A further set of numbers (13-17) for very strong winds were added by the US Weather Bureau in 1955.

The Beaufort Scale, as originally drawn up, made no reference to the speed of the wind and various attempts have been made to correlate the two.

The scale is not often used today as more direct methods are used by meteorologists to measure wind speed. However, it is still useful in estimating wind speeds, especially when anemometers are not available.

Other resources

Beaufort Scale from weather pages of Young America
Windsurfing calculator from Windsurfer.com
Beaufort Wind Force Scale Number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12
Wind speed (knots): 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70

Wind speed (kph): 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120

Sea Disturbance Number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Average wave height (m): 0, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16

Average wave height (ft): 0, 1, 2, 4, 10, 15, 20, 25, 30, 35, 40, 45, 50




Beaufort number 0 - Calm

Wind speeds: less than 1 knot (<1 mph; <1 kph; <0.3 mps)
At sea: Sea like a mirror, calm

Sea disturbance number: 0

Probable wave height: flat (0 ft; 0 m)

On land: Smoke rises vertically

Notes: Boring, boring, boring...

Go to Beaufort number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12



Beaufort number 1 - Light Air

Wind speeds: 1-3 knots (1-3 mph; 1-5 kph; 0.3-1.5 mps)
At sea: Ripples with the appearance of scales are formed but without foam crests

Sea disturbance number: 0

Probable wave height: 5-10 cm (2-4 in) (0 ft; 0 m)

On land: Direction of wind shown by smoke drift, but not by vanes

Notes: Yachts just have steerage way

Go to Beaufort number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12



Beaufort number 2 - Light Breeze

Wind speeds: 4-6 knots (4-7 mph; 6-11 kph; 1.6-3.3 mps)
At sea: Small wavelets, still short but more pronounced; crests have a glassy appearance and do not break

Sea disturbance number: 1

Probable wave height: 10-15 cm (4-6 in); (0-1 ft; 0-0.3 m)

On land: Wind felt on face; leaves rustle; ordinary vane moved by wind

Notes: Wind fills sails of yacht, which then may move at 1-2 knots

Go to Beaufort number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12



Beaufort number 3 - Gentle Breeze

Wind speeds: 7-10 knots (8-12 mph; 12-19 kph; 3.4-5.4 mps)
At sea: Large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses

Sea disturbance number: 2

Probable wave height: 60 cm (2 ft); (1-2 ft; 0.3-0.6 m)

On land: Leaves and small twigs in constant motion; wind extends light flag

Notes: Yachts start to careen and travel at 3-4 knots

Go to Beaufort number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12



Beaufort number 4 - Moderate Breeze

Wind speeds: 11-16 knots (13-18 mph; 20-28 kph; 5.5-7.9 mps)
At sea: small waves, becoming longer; fairly frequent white horses

Sea disturbance number: 3

Probable wave height: 1 m (3.5 ft); (2-4 ft; 0.6-1.2 m)

On land: Raises dust and loose paper; small branches are moved

Notes: Good working breeze for yachts; carry all sail with good list

Go to Beaufort number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12



Beaufort number 5 - Fresh Breeze

Wind speeds: 17-21 knots (19-24 mph; 29-38 kph; 8.0-10.7 mps)
At sea: Moderate waves taking a more pronounced long form; many white hourses are formed; chance of some spray

Sea disturbance number: 4

Probable wave height: 2 m (6-7 ft); (4-8 ft; 1.2-2.4 m)

On land: Small trees in leaf begin to sway; crested wavelets form on inland waters

Notes: Yachts shorten sail

Go to Beaufort number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12



Beaufort number 6 - Strong Breeze

Wind speeds: 22-27 knots (25-31 mph; 39-49 kph; 10.8-13.8 mps)
At sea: Large waves begin to form; the white foan crests are more extensive everywhere; probably some spray

Sea disturbance number: 5

Probable wave height: 3 m (9-10 ft); (8-13 ft; 2.4-4 m)

On land: Large branches in motion; whistling heard in telegraph wires; umbrellas used with dificulty

Notes: Yachts with double reef in mainsail; cared required when fishing

Go to Beaufort number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12



Beaufort number 7 - Near Gale / Moderate Gale

Wind speeds: 28-33 knots (32-38 mph; 50-61 kph; 13.9-17.1 mps)
At sea: Sea heaps up and white foam from the breaking waves begins to be blown in streaks along the direction of the wind

Sea disturbance number: 6

Probable wave height: 4 m (13-14 ft); (13-20 ft; 4-6 m)

On land: Whole trees in motion; inconvenience felt when walking against wind

Notes: Yachts remain in harbour, those at sea lie to

Go to Beaufort number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12



Beaufort number 8 - Gale / Fresh Gale

Wind speeds: 34-40 knots (39-46 mph; 62-74 kph; 17.2-20.7 mps)
At sea: Moderately high waves of greater length; edges crests begin to break into spindrift; the foam is blown in well-marked streaks along the direction of the wind

Sea disturbance number: 6

Probable wave height: 5.5 m (18 ft); (13-20 ft; 4-6 m)

On land: Breaks twigs off trees; generally impedes progress

Notes: All yachts make for harbour if possible

Go to Beaufort number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12



Beaufort number 9 - Strong Gale

Wind speeds: 41-47 knots (47-54 mph; 75-88 kph; 20.8-24.4 mps)
At sea: High waves; dense streaks of foam along the direction of wind; crests of waves begin to topple, tumble and roll over; spray may affect visibility

Sea disturbance number: 6

Probable wave height: 7 m (23 ft); (13-20 ft; 4-6 m)

On land: Slight structural damage occurs (chimney post and slates removed)

Notes:

Go to Beaufort number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12



Beaufort number 10 - Storm / Whole Gale

Wind speeds: 48-55 knots (55-63 mph; 89-102 kph; 24.5-28.4 mps)
At sea: 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 a white appearance; tumbling of the sea becomes heavy and shock-like; visibility affected

Sea disturbance number: 7

Probable wave height: 9 m (29 ft); (20-30 ft; 6-9 m)

On land: Seldom experienced inland; trees uprooted; considerable structural damage occurs

Notes:

Go to Beaufort number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12



Beaufort number 11 - Violent Storm / Storm

Wind speeds: 56-63 knots (64-75 mph; 103-117 kph; 28.5-32.6 mps)
At sea: Exceptionally high waves (small and medium size ships might be for a time lost from view behind waves); sea is completely covered with long white patches of foam lying along the direction of wind; everywhere the edges are blown into froth; visibility afected

Sea disturbance number: 8

Probable wave height: 11 m (37 ft); (30-45 ft; 9-14 m)

On land: Very rarely experienced; accompanied by widespread damage

Notes:

Go to Beaufort number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12



Beaufort number 12 (-17) - Hurricane

Wind speeds: 64 knots and greater (> 75 mph; >117 kph; >32.7 mps)
At sea: The air is filled with foam and spray; sea completely white with driving spray; visibility very seriously affected

Sea disturbance number: 9

Probable wave height: 11 m and more (> 37 ft); (>45 ft; >14 m)

On land: Very rarely experienced; accompanied by widespread damage

Notes:

Go to Beaufort number: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12