Wind speed is measured using the Beaufort Scale, see the table below.
| Force | Description | Speed | Notes | Probable Wave Height | Sea State | |||
|---|---|---|---|---|---|---|---|---|
| km/h | mph | knots | Meters | Max | ||||
| 0 | Calm | <1 | <1 | <1 | Smoke rises vertically, sea like a mirror. | -- | -- | 0 |
| 1 | Light Air | 1 to 5 | 1 to 3 | 1 to 3 | Direction shown by smoke drift but not by wind vanes, ripples on sea. | 0.1 | 0.1 | 1 |
| 2 | Light Breeze | 6 to 11 | 4 to 7 | 4 to 6 | Wind felt on face; leaves rustle; wind vane moved by wind. Small wavelets on sea | 0.2 | 0.3 | 2 |
| 3 | Gentle Breeze | 12 to 19 | 8 to 12 | 7 to 10 | Leaves and small twigs in constant motion; light flags extended. Large wavelets on sea. | 0.6 | 1.0 | 3 |
| 4 | Moderate Breeze | 20 to 28 | 13 to 18 | 11 to 16 | Raises dust and loose paper; small branches moved. Small waves, fairly frequent white horses | 1.0 | 1.5 | 3 to 4 |
| 5 | Fresh Breeze | 29 to 38 | 19 to 24 | 17 to 21 | Small trees in leaf begin to sway; crested wavelets form on inland waters. Moderate waves, many white horses | 2.0 | 2.5 | 4 |
| 6 | Strong Breeze | 38 to 49 | 25 to 31 | 22 to 27 | Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty. Large waves, extensive foam crests | 3.0 | 4.0 | 5 |
| 7 | Near Gale | 50 to 61 | 32 to 38 | 28 to 33 | Whole trees in motion; inconvenience felt when walking against the wind. Foam blown in streaks across the sea | 4.0 | 5.5 | 5 to 6 |
| 8 | Gale | 62 to 74 | 39 to 46 | 34 to 40 | Twigs break off trees; generally impedes progress. Wave crests begin to break into spindrift | 5.5 | 7.5 | 6 to 7 |
| 9 | Strong Gale | 75 to 88 | 47 to 54 | 41 to 47 | Slight structural damage (chimney pots and slates removed). Wave crests topple over, spray affects visibility | 7.0 | 10.0 | 7 |
| 10 | Storm | 89 to 102 | 55 to 63 | 48 to 55 | Seldom experienced inland; trees uprooted; considerable structural damage. Sea surface largely white | 9.0 | 12.6 | 8 |
| 11 | Violent Storm | 103 to 117 | 64 to 72 | 56 to 63 | Very rarely experienced; accompanied by widespread damage. Medium-sized ships lost to view behind waves. Sea covered in white foam, visibility seriously affected | 11.5 | 16.0 | 8 |
| 12 | Hurricane | 118+ | 73+ | 64+ | Devastation. Air filled with foam and spray, very poor visibility | 14+ | --- | 9 |