In the past, the wind speed was usually reported in knots until the Beaufort scale was developed in 1806 by the Royal Navy officer Francis Beaufort. The Lighthouse builder, John Smeaton, proposed in 1759 that the wind speed should be correlated with simple verbal descriptions, but this never caught on. A knot is equal to 1 nautical mile per hour, which is approximately 1.15 land miles or 1.85 kilometres an hour.
| Beaufort scale | Wind speed in knots | State of wind |
|---|---|---|
| 0 | 0-1 | calm |
| 1 | 2-3 | light air |
| 2 | 3-5 | light breeze |
| 3 | 5-10 | gentle breeze |
| 4 | 10-15 | moderate breeze |
| 5 | 15-20 | fresh breeze |
| 6 | 20-25 | strong breeze |
| 7 | 25-35 | moderate/near gale |
| 8 | 35-40 | (fresh) gale |
| 9 | 40-45 | strong gale |
| 10 | 45-55 | storm (whole gale) |
| 11 | 55-65 | great/violent storm |
| 12 | Over 65 | hurricane |
Source: Seamanship in the Age of Sail: An Account of Shiphandling of the Sailing Man-O-War, 1600-1860 by John Harland.