beaufort scale

The Beaufort Scale of Wind Force was developed in 1805 by Admiral Sir Francis Beaufort as a means for sailors to gauge wind speeds through visual observations of the sea state.

The scale runs from Force 0 (calm) to Force 12 (Hurricane).

Force Wind (Knots) Classification Wind Effect
0 <1 Calm Sea surface smooth and mirror-like.
1 1-3 Calm Scaly ripples, no foam crests.
2 4-6 Light Breeze Small wavelets, crests glassy, no breaking.
3 7-10 Gentle Breeze Large wavelets, crests begin to break, scattered whitecaps.
4 11-16 Moderate Breeze Small waves 1-4 ft. becoming longer, numerous whitecaps.
5 17-21 Fresh Breeze Moderate waves 4-8 ft taking longer form, many whitecaps, some spray.
6 22-27 Strong Breeze Larger waves 8-13 ft, whitecaps common, more spray.
7 28-33 Near Gale Sea heaps up, waves 13-20 ft, white foam streaks off breakers.
8 34-40 Gale Moderately high (13-20 ft) waves of greater length, edges of crests begin to break into spindrift, foam blown in streaks.
9 41-47 Strong Gale High waves (20 ft), sea begins to roll, dense streaks of foam, spray may reduce visibility.
10 48-55 Storm Very high waves (20-30 ft) with overhanging crests, sea white with densely blown foam, heavy rolling, lowered visibility.
11 56-63 Violent Storm Exceptionally high (30-45 ft) waves, foam patches cover sea, visibility more reduced.
12 64+ Hurricane Air filled with foam, waves over 45 ft, sea completely white with driving spray, visibility greatly reduced.

This is the scale that we use in our book Busy Doing Nothing.