Beaufort scale: force 0 to 12 you can see
A number in the shipping forecast means little until you know what it looks like. Move the slider: the Beaufort scale shows every force from 0 to 12 as a picture you can see, with the sea that comes with it and what it means on board.
4
knots
km/h
m/s
Wave (m)
Sea
On board
The Beaufort scale as a table
Tap a row and the picture above shows that force.
| Bft | Description | knots | km/h | Wave (m) | Sea |
|---|---|---|---|---|---|
| 0 | Calm | < 1 | < 1 | 0 | Sea like a mirror. |
| 1 | Light air | 1-3 | 1-5 | 0.1 | Ripples like scales, no foam crests. |
| 2 | Light breeze | 4-6 | 6-11 | 0.2 | Small wavelets, crests look glassy and do not break. |
| 3 | Gentle breeze | 7-10 | 12-19 | 0.6 | Crests begin to break, scattered white horses. |
| 4 | Moderate breeze | 11-16 | 20-28 | 1 | Longer waves, frequent white horses. |
| 5 | Fresh breeze | 17-21 | 29-38 | 2 | Moderate waves, white horses everywhere, some spray. |
| 6 | Strong breeze | 22-27 | 39-49 | 3 | Large waves, crests breaking, extensive white foam. |
| 7 | Near gale | 28-33 | 50-61 | 4 | Sea heaps up, foam blown in streaks downwind. |
| 8 | Gale | 34-40 | 62-74 | 5.5 | Moderately high waves, crests break into spindrift. |
| 9 | Strong gale | 41-47 | 75-88 | 7 | High waves, dense streaks of foam, spray cuts visibility. |
| 10 | Storm | 48-55 | 89-102 | 9 | Very high waves with overhanging crests, the sea turns white. |
| 11 | Violent storm | 56-63 | 103-117 | 11.5 | Exceptionally high waves, the sea covered in foam. |
| 12 | Hurricane force | ≥ 64 | ≥ 118 | ≥ 14 | Air full of foam and spray, the sea completely white. |
What the wave height means
The wave heights in the table apply to the open sea, once the wind has blown long enough over a wide stretch of water. Close inshore, in the Channel or on inland waters the waves stay lower but grow shorter and steeper, and that is what makes them hard work in a small boat. Wind against tide builds a short, steep sea on top.
Wind speeds and wave heights from the World Meteorological Organization. The picture is drawn and simplified.
