Wind Speed Converter

Wind speed is measured in several units worldwide: knots (nautical miles per hour) in aviation and maritime, km/h in most weather forecasts, mph in the United States, and m/s in scientific contexts. The Beaufort scale translates speed into observable descriptions of wind effects, which is useful when you don’t have instruments.

Conversion formulas: knots × 1.852 = km/h km/h × 0.621 = mph m/s × 3.6 = km/h mph × 0.447 = m/s

Beaufort Scale reference:

Worked example: A forecast shows 45 knots. 45 × 1.852 = 83.3 km/h = 51.7 mph → Beaufort 9 (Strong Gale)

Sustained wind is not gust speed, and the difference is bigger than people expect. Forecasts quote a sustained average, taken over ten minutes in most of the world and one minute in the United States. Gusts routinely run 20 to 40 percent above that, and gusts are what actually take fence panels off. If a forecast says 40 mph sustained, plan for something closer to 55.

Why the Beaufort numbers look uneven. The scale was written in 1805 by Francis Beaufort, a Royal Navy officer, and it originally described how much sail a ship could carry rather than any measured speed. The mph figures were fitted to it long afterwards, which is why the bands are not equal widths and why the descriptions are about trees and smoke rather than numbers. That turns out to be its lasting strength: you can estimate Force 6 by watching an umbrella fail, with no instrument at all.

One practical note on the converter above. Choosing Beaufort as the input unit returns the bottom of that force band, not a midpoint, so Force 8 gives 39 mph rather than the 42 or so a real Force 8 usually blows. Treat it as a floor.

The mph and km/h columns are rounded from the scale’s official definition, which is written in metres per second. That is why the top band starts at 73 mph here and at 32.7 m/s in the source: the same boundary, a sixth of a mile an hour apart. If you are converting for a turbine rather than a forecast, the wind speed unit converter works in m/s throughout and adds the sea state and the turbine power curve.