This scale was developed by Sir Francis Beaufort, around 1805 to gauge wind speed without the aid of instrumentation.

Force 1 applies where a 1-3 knot wind is observed producing light air. At sea you will observe small wavelets with crests of glassy appearance and on land leaves rustle and vanes begin to move.


Force 2 applies where a 4-6 knot wind is observed producing light breezes. At sea you will observe small wavelets with crests of glassy appearance and on land you will feel the wind in your face, leaves rustle and vanes begin to move.
Force 3 applies where a 7-10 knot wind is observed producing a gentle breeze. At sea you will observe large wavelets and crests will begin to break producing scattered whitecaps and on land leaves and small twigs are in in motion and light flags are extended.

 

Force 4 applies where a 11-16 knot wind is observed producing a moderate breeze. At sea you will observe 0.5-1.25 meter waves with numerous whitecaps and on land leaves and loose paper are raised up, flags flap and small branches move.

 

Force 5 applies where a 17-21 knot wind is observed producing a fresh breeze. At sea you will observe 1.25-2.5 meter waves with many whitecaps and some spray and on land small trees begin to sway and flags flap ripple.

 

Force 6 applies where a 22-27 knot wind is observed producing a strong breeze. At sea you will observe 2.5-4 meter waves whitecaps everywhere and more spray and on land large branches are in motion and you will hear whistling in wires.

 

Force 7 applies where a 28-33 knot wind is observed producing a near gale. At sea you will observe 4-6 meter waves with white foam blowing in streaks and on land whole trees are in motion and you will encounter resistance when walking against the wind.


Force 8 applies where a 34-40 knot wind is observed producing a gale. At sea you will observe 4-6 meter waves with the edges of their crests beginning to break and foam blowing in streaks and on land whole trees are in motion and you will encounter resistance when walking against the wind.


Force 9 applies where a 41-47 knot wind is observed producing a strong gale. At sea you will observe 4-6 meter waves and the sea begins to roll with dense steaks of foam and on land slight structural damage occurs with shingles blown of roofs.


Force 10 applies where a 48-55 knot wind is observed producing a storm. At sea you will observe 6-9 meter waves in a churning white sea with heavy rolling and reduced visibility and on land trees are broken or uprooted and considerable slight structural damage occurs.


Force 11 applies where a 56-63 knot wind is observed producing a violent storm. At sea you will observe 9-14 meter waves with white foam patches and reduced visibility and on land there is widespread damage and structures.


Force 12 applies where a 64+ knot wind is observed producing a hurricane. At sea you will observe 14+ meter waves while at sea with driving spray and visibility is seriously affected and on land there is severe and extensive damage.