| Beaufort number |
m/s |
knots |
Km/h |
Wind type |
Sea Conditions |
| 0 |
0.5 |
0-1 |
<2 |
Calm
|
Sea like a mirror |
| 1 |
0.5-1.5 |
1-3 |
2-5 |
Light air
|
Ripples with appearance of scales are formed, without foam crests |
| 2 |
1,6-3,3 |
4-6 |
6-11 |
Light breeze
|
Small wavelets still short but more pronounced; crests have a glassy appearance but do not break |
| 3 |
3.4-5.5 |
7-10 |
12-19 |
Gentle breeze
|
Large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses |
| 4 |
5.5-7.9 |
11-16 |
20-28 |
Moderate breeze
|
Small waves becoming longer; fairly frequent white horses |
| 5 |
8-10.7 |
17-21 |
29-38 |
Fresh breeze
|
Moderate waves taking a more pronounced long form; many white horses are formed; chance of some spray |
| 6 |
10.8-13.8 |
22-27 |
39-49 |
Strong breeze
|
Large waves begin to form; the white foam crests are more extensive everywhere; probably some spray |
| 7 |
13.9-17.1 |
28-33 |
50-61 |
Near gale
|
Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind; spindrift begins to be seen |
| 8 |
17.2–20.7 |
34-40 |
62-74 |
Gale
|
High waves of greater length; edges of crests break into spindrift; foam is blown in well-marked streaks along the direction of the wind |
| 9 |
20.8-24.4 |
41-47 |
75-88 |
Strong Gale
|
High waves; dense streaks of foam along the direction of the wind; sea begins to roll; spray affects visibility |
| 10 |
24.5-28.4 |
48-55 |
89-102 |
Storm
|
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 on a white appearance; rolling of the sea becomes heavy; visibility affected |
| 11 |
28.5-32.6 |
56-63 |
103-117 |
Violent Storm
|
Exceptionally high waves; small- and medium-sized ships might be for a long time lost to view behind the waves; sea is covered with long white patches of foam; everywhere the edges of the wave crests are blown into foam; visibility affected |
| 12 |
32.7+ |
64+ |
118+ |
Hurricane force |
The air is filled with foam and spray; sea is completely white with driving spray; visibility very seriously affected |