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Beaufort wind force scale

Specifications and equivalent speeds
Beaufort wind scale Mean Wind Speed Limits of wind speed Wind descriptive terms Probable wave height in metres* Probable maximum wave height in metres* Seastate Sea descriptive terms
Knots m/s Knots m/s
0 0 0 <1 0–0.2 Calm - - 0 Calm (glassy)
1 2 0.8 1–3 0.3–1.5 Light air 0.1 0.1 1 Calm (rippled)
2 5 2.4 4–6 1.6–3.3 Light breeze 0.2 0.3 2 Smooth (wavelets)
3 9 4.3 7–10 3.4–5.4 Gentle breeze 0.6 1.0 3 Slight
4 13 6.7 11–16 5.5–7.9 Moderate breeze 1.0 1.5 3–4 Slight–Moderate
5 19 9.3 17–21 8.0–10.7 Fresh breeze 2.0 2.5 4 Moderate
6 24 12.3 22–27 10.8–13.8 Strong breeze 3.0 4.0 5 Rough
7 30 15.5 28–33 13.9–17.1 Near gale 4.0 5.5 5–6 Rough–Very rough
8 37 18.9 34–40 17.2–20.7 Gale 5.5 7.5 6–7 Very rough–High
9 44 22.6 41–47 20.8–24.4 Severe gale 7.0 10.0 7 High
10 52 26.4 48–55 24.5–28.4 Storm 9.0 12.5 8 Very High
11 60 30.5 56–63 28.5–32.6 Violent storm 11.5 16.0 8 Very High
12 - - 64+ 32.7+ Hurricane 14+ - 9 Phenomenal

*

  1. These values refer to well-developed wind waves of the open sea.
  2. The lag effect between the wind getting up and the sea increasing should be borne in mind.