The Beaufort Scale provides a useful means for estimating wind strength in the field.
The scale consists of 13 categories (range 0 - 12) which cover the full range of wind speeds likely to be encountered inland or at sea.
The category descriptions allow windspeed (as a Beaufort Force) to be estimated without requiring instruments or detailed meterological knowledge.
| Force | Description | Wind speed | Conditions on Land | Notes | |
|---|---|---|---|---|---|
| 0 | Calm | 0 - 1 km/h | 0 - 1 mph | Smoke rises vertically. | |
| 1 | Light air | 1 - 5 km/h | 1 - 3 mph | Smoke drifts slowly. | |
| 2 | Light breeze | 6 - 11 km/h | 4 - 7 mph | Wind felt on face; leaves rustle. | |
| 3 | Gentle breeze | 12 - 19 km/h | 8 - 12 mph | Leaves and small twigs move constantly; light flags extended. | |
| 4 | Moderate breeze | 20 - 29 km/h | 13 - 18 mph | Dust and small branches move; flags flap. | |
| 5 | Fresh breeze | 30 - 39 km/h | 19 - 24 mph | Small leafy trees begin to sway; flags ripple; crested wavelets on inland waters. | |
| 6 | Strong breeze | 40 - 49 km/h | 25 - 31 mph | Large branches move; flags beat; wires whistle; umbrellas are difficult to control. | |
| 7 | Near gale | 50 - 61 km/h | 32 - 38 mph | Whole trees in motion; flags extended; inconvenience walking against wind. | |
| 8 | Gale | 62 - 74 km/h | 39 - 46 mph | Twigs and small branches blown off trees; walking generally impeded. | |
| 9 | Strong gale | 75 - 88 km/h | 47 - 54 mph | Slight structural damage (eg. slates blown off roofs). | |
| 10 | Storm | 89 - 102 km/h | 55 - 63 mph | Trees uprooted; considerable structural damage. | (1) |
| 11 | Violent storm | 103 - 117 km/h | 64 - 72 mph | Widespread damage to structures. | (2) |
| 12 | Hurricane | 118 - 134 km/h | 73 - 82 mph | Severe structural damage to buildings; wide-spread devastation. | (2) |
Notes:
| Force | Description | Wind speed | Conditions at Sea (1) | Notes | |
|---|---|---|---|---|---|
| 0 | Calm | 0 - 1 km/h | 0 - 1 mph | Sea like a mirror. | |
| 1 | Light air | 1 - 5 km/h | 1 - 3 mph | Ripples only. | |
| 2 | Light breeze | 6 - 11 km/h | 4 - 7 mph | Small wavelets (0.2 m). Crests have a glassy appearance. | |
| 3 | Gentle breeze | 12 - 19 km/h | 8 - 12 mph | Large wavelets (0.6 m); crests begin to break. | |
| 4 | Moderate breeze | 20 - 29 km/h | 13 - 18 mph | Small waves (1 m); some whitecaps. | |
| 5 | Fresh breeze | 30 - 39 km/h | 19 - 24 mph | Moderate waves (1.8 m); many whitecaps. | |
| 6 | Strong breeze | 40 - 49 km/h | 25 - 31 mph | Large waves (3 m); probably some spray. | |
| 7 | Near gale | 50 - 61 km/h | 32 - 38 mph | Mounting sea (4 m) with foam blown in streaks downwind. | |
| 8 | Gale | 62 - 74 km/h | 39 - 46 mph | Moderately high waves (5.5 m); crests break into spindrift. | |
| 9 | Strong gale | 75 - 88 km/h | 47 - 54 mph | High waves (7 m); dense foam; visibility affected. | |
| 10 | Storm | 89 - 102 km/h | 55 - 63 mph | Very high waves (9 m); heavy sea roll; visibility impaired. Surface generally white. | |
| 11 | Violent storm | 103 - 117 km/h | 64 - 72 mph | Exceptionally high waves (11 m); visibility poor. | |
| 12 | Hurricane | 118 - 134 km/h | 73 - 82 mph | 14 m waves; air filled with foam and spray; visibility bad. | (2) |
Notes:
The Beaufort scale was originally created in 1805 by Admiral Sir Francis Beaufort (1774-1857), by standardising a number of existing methods. It has since been adapted slightly to fit various technological advances. More details may found at on wikipedia and various other sites.