In 1805, British Admiral Sir Francis Beaufort developed this wind scale to help sailors estimate the speed of the wind using visual observations. The scale starts with 0 and extends to a force of 12.

Force	Description	Winds	Signs
0	Calm	0 mph (0 kph)	Smoke rises vertically.
1	Light air	1–3 mph (1–5 kph)	Smoke drifts, but wind vanes or flags do not move.
2	Slight breeze	4–7 mph (6–11 kph)	Leaves rustle and wind vanes move.
3	Gentle breeze	8–12 mph (12–19 kph)	Leaves and small twigs are in constant motion; flags are extended.
4	Moderate breeze	13–18 mph (20–29 kph)	Dust and loose paper blow; small branches move in trees.
5	Fresh breeze	19–24 mph (30–39 kph)	Small leafy trees begin to sway.
6	Strong breeze	25–31 mph (40–50 kph)	Large branches are in motion; whistling is heard in utility wires.
7	Moderate gale	32–38 mph (51–61 kph)	Whole trees are in motion; it is difficult to walk against the wind.
8	Fresh gale	39–46 mph (62–74 kph)	Twigs break from trees.
9	Strong gale	47–54 mph (75–87 kph)	Roof shingles blow free; slight structural damage can occur.
10	Whole gale	55–63 mph (88–101 kph)	Trees are broken or uprooted; considerable structural damage occurs.
11	Storm	64–73 mph (102–118 kph)	Widespread damage occurs; trees blow a distance.
12	Hurricane	74+ mph (119+ kph)	Extreme destruction occurs; buildings are destroyed, trees and utilities are down.