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Beaufort to m/s Converter

Enter a Beaufort wind force number from 0 to 12.

How it is calculated

Enter a Beaufort force number. The tool uses the empirical relation v = 0.836 × B1.5, where B is the Beaufort number and v is the wind speed in metres per second, then km/h = v × 3.6. Both are shown with two decimals. It gives one representative speed for the number, not the speed range that a printed Beaufort table lists for each force. Decimals such as 4.5 are accepted, and the allowed range is 0 to 17; anything below 0 or above 17 gives no result. A short label comes with the result: Calm below 1, Light for 1-3, Moderate for 4-5, Strong for 6-7, Gale for 8-9 and Storm for 10 and above, so force 12 is labelled just Storm.

Worked example

A marine forecast warns of force 6. Raise 6 to the power 1.5: 61.5 = 6 × √6 = 6 × 2.4495 = 14.697. Multiply by 0.836: 0.836 × 14.697 = 12.29 m/s, shown as 12.29 m/s. For kilometres per hour multiply by 3.6: 12.29 × 3.6 = 44.23 km/h. Force 6 falls in the 6-7 band, so the label is Strong. As a check, force 12 gives 34.75 m/s, about 125 km/h.

Try this example →

Common mistakes

  • Treating the output as an exact measured speed. The Beaufort scale describes ranges of wind, and the formula returns a typical value in the middle; the real wind in a given force can be above or below it.
  • Entering a wind speed instead of a force number. The field takes a Beaufort number, so typing 25 (as m/s or km/h) gives no result because it is above 17.
  • Using the label as the official scale name. The tool's five bands are a simplification, so force 8 and 9 both read Gale, while the full scale distinguishes more steps.
  • Confusing m/s with knots or mph. Forecast speeds are often in knots, so convert before comparing; the output here is only m/s and km/h.
  • Assuming the speed rises evenly with the force. It follows B1.5, so each step at the high end adds far more speed than a step at the low end.

About this calculator

The Beaufort scale is a 0-to-12 system devised in 1805 by Royal Navy officer Francis Beaufort to estimate wind force from observable effects — force 0 is "calm, smoke rises vertically," force 6 is "large branches move, umbrellas used with difficulty," and force 12 is hurricane-force wind. This calculator converts a given Beaufort number (0 to 17) into a single typical wind speed in meters per second and km/h, using the formula v = 0.836 × B^1.5, along with a one-word description of the wind (calm, light, moderate, strong, gale or storm). Because it returns one formula value rather than the scale's official speed band, treat the result as an approximation.

Though modern anemometers measure wind speed directly, the Beaufort scale remains standard in marine and maritime weather forecasting — shipping forecasts and small-craft advisories are still commonly issued in Beaufort force — and sailors, fishers, and coastal weather watchers use conversions like this one to translate a forecast's Beaufort number into a concrete speed they can plan around.

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  • Editorial team

    Forecasts in knots are easy to compare once you remember that 1 m/s is about 1.94 knots. Force 6 comes out here as 12.29 m/s, roughly 23.9 knots, which falls inside the 22 to 27 knot band the printed Beaufort table lists for that force. Treat the single number as a midpoint and expect gusts above it. Would you like knots shown alongside m/s and km/h? Tell us which unit your forecasts use.

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