There is one scale for land and one for maritime. It was created by Rear Admiral Sir Francis Beaufort (1774-1857). In 1955, The U.S. Weather Bureau added forces 13 to 17 to indicate higher wind strengths as in tropical storms, but their usage has been limited.
Force Description | knots | km/h | mph |
|
<1 1-3 4-6 7-10 11-16 17-21 22-27 28-33 34-40 41-47 48-55 56-63 64+ |
<1 1-5 6-11 12-19 20-29 30-39 40-50 51-61 62-74 75-87 88-101 102-117 118+ |
<1 1-3 4-7 8-12 13-18 19-24 25-31 32-38 39-46 47-54 55-63 64-73 74+ |