Wind speed is measured using the Beaufort Scale, see the table below.

ForceDescriptionSpeedNotesProbable Wave
Sea State
0Calm<1<1<1Smoke rises vertically, sea like a mirror.----0
1Light Air1 to 51 to 31 to 3Direction shown by smoke drift but not by wind vanes, ripples on sea.0.10.11
2Light Breeze6 to 114 to 74 to 6Wind felt on face; leaves rustle; wind vane moved by wind. Small wavelets on sea0.20.32
3Gentle Breeze12 to 198 to 127 to 10Leaves and small twigs in constant motion; light flags extended. Large wavelets on sea.0.61.03
4Moderate Breeze20 to 2813 to 1811 to 16Raises dust and loose paper; small branches moved. Small waves, fairly frequent white horses1.01.53 to 4
5Fresh Breeze29 to 3819 to 2417 to 21Small trees in leaf begin to sway; crested wavelets form on inland waters. Moderate waves, many white horses2.02.54
6Strong Breeze38 to 4925 to 3122 to 27Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty. Large waves, extensive foam crests3.04.05
7Near Gale50 to 6132 to 3828 to 33Whole trees in motion; inconvenience felt when walking against the wind. Foam blown in streaks across the sea4.05.55 to 6
8Gale62 to 7439 to 4634 to 40Twigs break off trees; generally impedes progress. Wave crests begin to break into spindrift5.57.56 to 7
9Strong Gale75 to 8847 to 5441 to 47Slight structural damage (chimney pots and slates removed). Wave crests topple over, spray affects visibility7.010.07
10Storm89 to 10255 to 6348 to 55Seldom experienced inland; trees uprooted; considerable structural damage. Sea surface largely white9.012.68
11Violent Storm103 to 11764 to 7256 to 63Very rarely experienced; accompanied by widespread damage. Medium-sized ships lost to view behind waves. Sea covered in white foam, visibility seriously affected11.516.08
12Hurricane118+73+64+Devastation. Air filled with foam and spray, very poor visibility14+---9