PHOTOS 07-09 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 mph Knots m/s mph Knots m/s 0 0 0 0 <1 <1 0-0.2 Calm - - 0 Calm (glassy) 1 2.3 2 0.8 1-4 1-3 0.3-1.5 Light air 0.1 0.1 1 Calm (rippled) 2 5.8 5 2.4 4-7 4-6 1.6-3.3 Light breeze 0.2 0.3 2 Smooth (wavelets) 3 10.4 9 4.3 8-12 7-10 3.4-5.4 Gentle breeze 0.6 1.0 3 Slight 4 15 13 6.7 13-18 11-16 5.5-7.9 Moderate breeze 1.0 1.5 3-4 Slight-Moderate 5 21.9 19 9.3 19-24 17-21 8.0-10.7 Fresh breeze 2.0 2.5 4 Moderate 6 27.6 24 12.3 25-31 22-27 10.8-13.8 Strong breeze 3.0 4.0 5 Rough 7 34.5 30 15.5 32-38 28-33 13.9-17.1 Near gale 4.0 5.5 5-6 Rough-Very rough 8 42.6 37 18.9 39-46 34-40 17.2-20.7 Gale 5.5 7.5 6-7 Very rough-High 9 50.7 44 22.6 47-54 41-47 20.8-24.4 Severe gale 7.0 10.0 7 High 10 60 52 26.4 55-63 48-55 24.5-28.4 Storm 9.0 12.5 8 Very High 11 69 60 30.5 64-72 56-63 28.5-32.6 Violent storm 11.5 16.0 8 Very High 12 - - 73+ 64+ 32.7+ Hurricane 14+ - 9 Phenomenal * i. These values refer to well-developed wind waves of the open sea. ii. The lag effect between the wind getting up and the sea increasing should be borne in mind
