The Beaufort scale is the standard system for classifying wind speed, ranging from Force 0 (calm, <1 km/h) to Force 12 (hurricane, >118 km/h). It was developed in 1805 by Royal Navy Admiral Sir Francis Beaufort based on the effect of wind on a fully rigged man-of-war's sails. In 1946, the WMO adopted it as the international standard, extending descriptions to include land-based observations.
Each force level is defined by observable effects: Force 3 (gentle breeze) makes leaves and twigs move constantly; Force 6 (strong breeze) makes large branches sway and umbrellas difficult to use; Force 8 (gale) breaks twigs from trees and makes walking against the wind difficult; Force 10 (storm) uproots trees and causes structural damage. At sea, the scale describes wave states from glassy calm (Force 0) to enormous waves with overhanging crests (Force 12).
Despite the universal availability of anemometers, the Beaufort scale remains invaluable because it allows anyone to estimate wind speed from visual observations. Mariners, pilots, hikers, and meteorologists all use it as a quick reference. Wind force is reported in SYNOP observations and marine forecasts worldwide. Spain's AEMET issues maritime warnings based on Beaufort force thresholds (Force 7+ for warnings, Force 9+ for severe warnings). Extended versions of the scale — Force 13 to 17 — are used in some Asian countries for typhoon-force winds but are not officially recognised by the WMO.