How beaufort scale calculator works
Admiral Francis Beaufort's 1805 scale rates wind by observable effects rather than an anemometer: force 0 is smoke rising vertically, force 6 is large branches swaying and umbrella trouble, force 12 is devastation with the air full of foam and spray. Each of the 13 forces maps to a published speed range in knots, km/h, mph and m/s, to a sea-state description, to a land description and to a probable wave height.
Enter a wind speed in any of the four units and the calculator matches it against the published boundary table for that unit — the half-open ranges the Met Office and WMO tables print — to return the force number and name. Choose the reverse direction and any force from 0 to 12 returns its full speed range in all four units plus the sea state, land signs and wave height.
The per-unit tables are the published ones, which means edges can disagree by a hair: the ranges were rounded independently when the scale was standardised, so 8.0 m/s opens force 5 in the m/s table while 15.55 knots (the same speed) still sits inside force 4 in the knot table. That is a quirk of the historical record, not a bug — the calculator reports what the official tables say for the unit you enter. All math runs in your browser.