An expanded Beaufort Scale of wind
based on WMO Guide to Meteorological Instrument and Observing Practice
| Beaufort Number | Desc. | Velocity equivalent at a standard height of 10 metres above open flat ground | Specifications for estimating speed over land | Description of Sea | Sea State | Significant Sea Wave Height in Metres | |||
| knots | mps | kmph | mph | ||||||
| 0 | Calm | < 1 | 0 - 0.2 | < 1 | < 1 | Calm; smoke rises vertically. | Sea like a mirror. | Calm (glassy) | 0 |
| 1 | Light air | 1 - 3 | 0.3 - 1.5 | 1 - 5 | 1 - 3 | Direction of wind shown by smoke- drift but not by wind vanes. | Ripples withthe appearance of scales are formed, but without foam crests. | Calm (rippled) | < 0.1 |
| 2 | Light breeze | 4 - 6 | 1.6 - 3.3 | 6 - 11 | 4 - 7 | Wind felt on face; leaves rustle; ordinary vanes moved by wind. | Small wavelets, still short but more pronounced; crests have a glassy appearance and do not break. | Smooth | 0.1 - 0.4 |
| 3 | Gentle breeze | 7 - 10 | 3.4 - 5.4 | 12 - 19 | 8 - 12 | Leaves and small twigs in constant motion; wind extends light flag. | Large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses. | Slight | 0.4 - 1.0 |
| 4 | Moderate breeze | 11 - 16 | 5.5 - 7.9 | 20 - 28 | 13 - 18 | Raises dust and loose paper; small branches are moved. | Small waves, becoming longer; fairly frequent white horses. | Slight/ Moderate | 1.0 - 1.6 |
| 5 | Fresh breeze | 17 - 21 | 8.0 - 10.7 | 29 - 38 | 19 - 24 | Small trees in leaf begin to sway,crested wavelets form on inland waters. | Moderate waves, taking a more pronounced long form; many white horses are formed (chance of some spray). | Moderate | 1.6 - 2.5 |
| 6 | Strong breeze | 22 - 27 | 10.8 - 13.8 | 39 - 49 | 25 - 31 | Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty. | Large waves begin to form; the white foam crests are more extensive everywhere (probably some spray). | Rough | 2.5 - 4.0 |
| 7 | Near gale | 28 - 33 | 13.9 - 17.1 | 50 - 61 | 32 - 38 | Whole trees in motion; inconvenience felt when walking against the wind. | Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind. | Very Rough | 4.0 - 6.0 |
| 8 | Gale | 34 - 40 | 17.2 - 20.7 | 62 - 74 | 39 - 46 | Breaks twigs off trees; generally impedes progress. | Moderately high waves of greater length; edges of crests begin to break into the spindrift; the foam is blown in well-marked streaks along the direction of the wind. | Very Rough to High | 6.0 - 7.5 |
| 9 | Strong gale | 41 - 47 | 20.8 - 24.4 | 75 - 88 | 47 - 54 | Slight structural damage occurs (chimney-pots and slates removed). | High waves; dense streaks of foam along the direction of the wind; crests of waves begin to topple, tumble and roll over; spray may affect visibility. | High | 7.5 - 9.0 |
| 10 | Storm | 48 - 55 | 24.5 - 28.4 | 89 - 102 | 55 - 63 | Seldom experienced inland; trees uprooted; considerable structural damage occurs. | Very high waves with long over- hanging crests; the resulting foam, in great patches, is blown in dense white streaks along the direction of the wind; on the whole, the surface of the sea takes a white appearance; the tumbling of the sea becomes heavy and shock- like; visibility affected. | Very High | 9.0 - 11.5 |
| 11 | Violent storm | 56 - 63 | 28.5 - 32.6 | 103 - 117 | 64 - 72 | Very rarely experienced; accompanied by widespread damage. | Exceptionally high waves (small and medium-sized ships might be for a time lost to view behind the waves); the sea is completely covered with long white patches of foam lying along the direction of the wind; everywhere the edges of the wave crests are blown into froth; visibility affected. | Very High | 11.5 - 14.0 |
| 12 | Hurricane | 64 - 71 | 32.7 - 36.9 | 118 - 133 | 73 - 82 | * | The air is filled with foam and spray; sea completely white with driving spray; visibility very seriously affected. | Phenomenal | > 14.0 |
| 13 | - | 72 - 80 | 37.0 - 41.4 | 134 - 149 | 83 - 92 | * | - | - | |
| 14 | - | 81 - 89 | 41.5 - 46.1 | 150 - 166 | 93 - 103 | * | - | - | |
| 15 | - | 90 - 99 | 46.2 - 50.9 | 167 - 183 | 104 - 114 | * | - | - | |
| 16 | - | 100 - 108 | 51.0 - 56.0 | 184 - 201 | 115 - 125 | * | - | - | |
| 17 | - | 109 - 118 | 56.1 - 61.2 | 202 - 220 | 126 - 136 | * | - | - | |
* The equivalents for speeds over 63 knots are provided for use when instrumental determination of speed is possible.