The Beaufort Scale
How is wind speed measured?
The Beaufort Scale is an empirical measure that relates wind speed to observed conditions at sea or on land. Its full name is the Beaufort wind force scale.
Below is a table showing the Beaufort Scale with speeds in knots, miles per hour and kilometers per hour. Please note that these are these are mean speeds, usually averaged over 10 minutes by convention, and do not capture the speed of wind gusts.
The quoted wind speed is that measured at 10 m above ground, not at the surface (which, at 2 m, may be only 50-70% of these figures)
|0||Calm||<1||<1||<1||Smoke rises vertically|
|1||Light Air||1-5||1-3||1-3||Direction shown by smoke drift but not by wind vanes|
|2||Light Breeze||6-11||4-7||4-6||Wind felt on face; leaves rustle; wind vane moved by wind|
|3||Gentle Breeze||12-19||8-12||7-10||Leaves and small twigs in constant motion; light flags extended|
|4||Moderate Breeze||20-28||13-18||11-16||Raises dust and loose paper; small branches moved.|
|5||Fresh Breeze||29-38||19-24||17-21||Small trees in leaf begin to sway; crested wavelets form on inland waters.|
|6||Strong Breeze||38-49||25-31||22-27||Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty.|
|7||Near Gale||50-61||32-38||28-33||Whole trees in motion; inconvenience felt when walking against the wind.|
|8||Gale||62-74||39-46||34-40||Twigs break off trees; generally impedes progress.|
|9||Strong Gale||75-88||47-54||41-47||Slight structural damage (chimney pots and slates removed).|
|10||Storm||89-102||55-63||48-55||Seldom experienced inland; trees uprooted; considerable structural damage|
|11||Violent Storm||103-117||64-72||56-63||Very rarely experienced; accompanied by widespread damage.|
|12||Hurricane||118 plus||73 plus||64 plus||Devastation|