| Scale | Knots | Wave Height | Surroundings |
|---|---|---|---|
| Force 0 Calm |
< 1 Knot | 0 | Sea is like a mirror |
| Force 1 Light Air |
1-3 | .25ft (.1M) |
Ripples with the appearance of scales, but without foam crests |
| Force 2 Light Breeze |
4-6 | .5-1ft (.2-.3M) |
Small wavelets, crests have a glassy appearance and do not break |
| Force 3 Gentle Breeze |
7-10 | 2-3ft (.6-1M) |
Large wavelets, crests begin to break, any foam has a glassy appearance, scattered whitecaps |
| Force 4 Moderate Breeze |
11-16 | 3.5-5ft (1-1.5M) |
Small waves becoming longer, fairly frequent white horses |
| Force 5 Fresh Breeze |
17-21 | 6-8ft (2-2.5M) |
Moderate waves take more pronounced long form, many white horses, chance of some spray |
| Force 6 Strong Breeze |
22-27 | 9.5-13ft (3-4M) |
Larger waves begin to form, spray is present, white foam crests are everywhere |
| Force 7 Near Gale |
28-33 | 13.5-19ft (4-5.5) |
Sea heaps up, white foam from breaking waves begins to be blown in streaks along the wind direction |
| Force 8 Gale |
34-40 | 18-25ft (5.5-7.5M) |
Moderately high waves of greater length, edges of crests begin to break into the spindrift, foam blown in well marked streaks along wind direction |
| Force 9 Strong Gale |
41-47 | 23-32ft (7-10) |
High waves, dense streaks of foam along direction of wind, wave crests begin to topple, tumble and roll over, spray may affect visibility |
| Force 10 Storm |
48-55 | 29-41ft (9-12.5M) |
Very high waves with very long overhanging crests, the resulting foam, in great patches, is blown in dense white streaks along wind direction. On the whole, sea surface takes a white appearance, tumbling of the sea is heavy and shock-like, visibility affected |
| Force 11 Violent Storm |
56-63 | 37-52ft (11.5-16M) |
Exceptionally high waves, small to medium sized ships may be lost to view behind the waves. Sea completed covered with long white patches of foam lying along wind direction. Everywhere, the edges of waves crests are blown into froth |
| Force 12 Hurricane |
64 | > 53ft (> 16M) |
Sea completely white with driving spray, visibility very seriously affected. The air is filled with foam and spray |
