Beaufort Scale Calculator

It is a 0 to 12 scale that links wind speed to the look of the sea and land. Force 0 is dead calm and force 12 is hurricane-force wind with towering seas. This tool maps a knot speed to its force, description and typical wave height.

Force 0 is under 1 knot, 1 is 1 to 3, 2 is 4 to 6, 3 is 7 to 10, 4 is 11 to 16, 5 is 17 to 21, 6 is 22 to 27, 7 is 28 to 33, 8 is 34 to 40, 9 is 41 to 47, 10 is 48 to 55, 11 is 56 to 63, and 12 is 64 knots or more.

A gale is force 8, which is 34 to 40 knots of sustained wind. Force 7 (28 to 33 knots) is a near gale and force 9 (41 to 47 knots) is a strong gale, so gale warnings cover this upper band.

No. The listed heights are the WMO probable open-sea values for a fully developed sea. Real waves depend on how long and how far the wind has blown, the fetch, plus water depth and current, so sheltered or shallow water sees smaller waves.

Use the sustained wind, which is usually a 10 minute average. Gusts are higher and brief, so entering a gust reads a higher force than the steady conditions actually justify.

Convert to knots first, then enter that. Divide miles per hour by about 1.151, or kilometres per hour by 1.852. For example 29 mph is about 25 knots, which is force 6.

Each force starts at its lower bound and runs up to just below the next one. The lower bound is included, so exactly 22 knots is force 6, not force 5, matching the ranges in the table.

Yes. Decimals are accepted and zero returns force 0, calm. The only invalid entries are blank fields, non-numbers and negative speeds, which show a prompt instead of a result.

It reports the sea-state description and wave height rather than the land observations like smoke drift or moving branches. The force number is the same on land and at sea, so you can cross-reference a land table using the force.