In 1806 Admiral Sir Francis Beaufort of the British Navy devised a wind velocity scale to enable the captains of sailing ships to accurately assess wind speeds at sea. Though the original scale dealt with purely maritime effects, it has since been modified for land by the National Weather Service.

Wind Force 0 0 Less then 1 Calm Smoke rises vertically.
Wind Force 1 1 1-3 Light air Direction of wind shown by smoke drift.
Wind Force 2 2 4-7 Light breeze Wind felt on face, leaves rustle.
Wind Force 3 3 8-12 Gentle breeze Leaves and small twigs in constant motion, wind extends flag.
Wind Force 4 4 13-18 Moderate breeze Wind raises dust and loose paper, small branches move.
Wind Force 5 5 19-24 Fresh breeze Small trees in leaf start to sway.
Wind Force 6 6 25-31 Strong breeze Large branches in motion, umbrellas used with difficulty.
Wind Force 7 7 32-38 Near gale Whole trees in motion, inconvenient to walk against wind.
Wind Force 8 8 39-47 Gale Twigs break from trees, difficult to walk.
Wind Force 9 9 48-54 Strong gale Slight structural damage occurs, slates removed.
Wind Force 10 10 55-63 Storm Trees uprooted, considerable structural damage.
Wind Force 11 11 64-72 Violent storm Widespread damage.
Wind Force 12 12 Greater then 72 Hurricane Widespread severe damage.