The Beaufort Scale of Wind Speed and Effect
Force Wind
(Knots)
Classification Wind Effect
0 less than 1 Calm Sea surface smooth and mirror-like
1 1 to 3 Light Air Scaly ripples, no foam crests
2 4 to 6 Light Breeze Small wavelets, crests glassy, no breaking
3 7 to 10 Gentle Breeze Large wavelets, crests begin to break, scattered whitecaps
4 11 to 16 Moderate Breeze Small waves 1-4 ft. becoming longer, numerous whitecaps
5 17 to 21 Fresh
Breeze
Moderate waves 4-8 ft taking longer form, many whitecaps, some spray
6 22 to 27 Strong Breeze Larger waves 8-13 ft, whitecaps common, more spray
7 28 to 33 Near Gale Sea heaps up, waves 13-20 ft, white foam streaks off breakers
8 34 to 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 to 47 Strong
Gale
High waves (20 ft), sea begins to roll, dense streaks of foam, spray may reduce visibility
10 48 to 55 Storm Very high waves (20-30 ft) with overhanging crests, sea white with densely blown foam, heavy rolling, lowered visibility
11 56 to 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
(Feel free to copy and print out this chart - courtesy of The Frugal-Mariner.com)