What is the Beaufort Scale?

The Beaufort wind force scale, or simply Beaufort scale, was devised at the beginning of the 19th century (around 1805) to provide a standard measure of wind speeds for sailors. It was subsequently extended for land use about a century later, in 1906, by George Simpson. The Beaufort scale is one wind scale among many that had been developed at the time, but after it became the mandatory standard for measuring wind speeds in the Royal Navy in 1838, the scale continued to stick, as it does to this day.

The Beaufort scale has 12 degrees, ranging from calm air to hurricane-force winds. In 1969 stages 13-17 were added for special cases such as especially strong tempests and hurricanes, although this scale is usually separately called the Saffir-Simpson Hurricane Scale.

Starting from 0 corresponding to calm, the Beaufort scale ascends to light air at 1, light breeze at 2, gentle breeze at 3, moderate breeze at 4, fresh breeze at 5, strong breeze at 6, near gale at 7, gale at 8, strong gale at 9, storm at 10, violent storm at 11, and hurricane at 12.

The Beaufort scale became popularized partially thanks to the invention of the telegraph in 1837 by Samuel Morse, and the cup anemometer in 1846 by T.R. Robinson. The cup anemometer is a hollowed-out half-sphere that spins at a given revolutions per minute depending on wind strength. These two inventions allowed wind speeds to be empirically measured and communicated across long distance, permitting storm warnings. This became particularly desirable after a naval war between the French and English in 1854 where many ships were lost due to severe storms.

Although the Beaufort scale continued to be used throughout the 19th century, there was no standard way of connecting cup anemometer revolutions to a given wind force degree, with more than 30 disagreeing scales being used throughout the world. It was not until 1926 than a uniform scale was established, with slight modifications in 1946. The Beaufort scale is still in use today, but many mariners simply measure wind speed in knots.