Reference
Beaufort and sea state scales
The Beaufort wind scale with speeds, what the sea looks like and the wave heights to expect, and the Douglas sea state code used in weather reports and logbooks.
Beaufort scale
| Force | Knots | m/s | Description | Sea | Waves, m (max) |
|---|---|---|---|---|---|
| 0 | < 1 | 0–0.2 | Calm | Sea like a mirror. | – |
| 1 | 1–3 | 0.3–1.5 | Light air | Ripples like scales, no foam crests. | 0.1 (0.1) |
| 2 | 4–6 | 1.6–3.3 | Light breeze | Small wavelets; crests glassy, not breaking. | 0.2 (0.3) |
| 3 | 7–10 | 3.4–5.4 | Gentle breeze | Large wavelets; crests begin to break; perhaps scattered white horses. | 0.6 (1) |
| 4 | 11–16 | 5.5–7.9 | Moderate breeze | Small waves becoming longer; fairly frequent white horses. | 1 (1.5) |
| 5 | 17–21 | 8.0–10.7 | Fresh breeze | Moderate, longer waves; many white horses; chance of some spray. | 2 (2.5) |
| 6 | 22–27 | 10.8–13.8 | Strong breeze | Large waves; white foam crests everywhere; probably some spray. | 3 (4) |
| 7 | 28–33 | 13.9–17.1 | Near gale | Sea heaps up; white foam from breaking waves blown in streaks. | 4 (5.5) |
| 8 | 34–40 | 17.2–20.7 | Gale | Moderately high, longer waves; crests break into spindrift; well-marked streaks of foam. | 5.5 (7.5) |
| 9 | 41–47 | 20.8–24.4 | Strong gale | High waves; dense streaks of foam; crests topple and roll over; spray may affect visibility. | 7 (10) |
| 10 | 48–55 | 24.5–28.4 | Storm | Very high waves with long overhanging crests; the sea looks white; heavy tumbling; visibility affected. | 9 (12.5) |
| 11 | 56–63 | 28.5–32.6 | Violent storm | Exceptionally high waves; the sea is covered with long white patches of foam; visibility affected. | 11.5 (16) |
| 12 | 64 + | 32.7 + | Hurricane | The air is filled with foam and spray; sea completely white with driving spray; visibility very seriously affected. | 14 + |
Douglas sea state
| Code | Sea | Wave height, m |
|---|---|---|
| 0 | Calm (glassy) | 0 |
| 1 | Calm (rippled) | 0–0.1 |
| 2 | Smooth (wavelets) | 0.1–0.5 |
| 3 | Slight | 0.5–1.25 |
| 4 | Moderate | 1.25–2.5 |
| 5 | Rough | 2.5–4 |
| 6 | Very rough | 4–6 |
| 7 | High | 6–9 |
| 8 | Very high | 9–14 |
| 9 | Phenomenal | over 14 |
Good to know
Wind speed is the mean over 10 minutes at 10 m above the sea. The wave heights are a guide for the open sea, far from land, once the sea has built up; in enclosed waters or near the coast waves are lower and steeper, and swell from elsewhere comes on top.
To turn the wind you measure on board into true wind, use the true wind calculator.
A summary for study and quick reference. The official texts (the International Code of Signals, COLREGs and their national versions) govern.
More tools
All tools- Port to port distances
- Compass error
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