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Beaufort Wind Scale Calculator

Find the Beaufort force and description for a wind speed.

Result

6
Strong breeze
11.11 m/s

How it is calculated

Enter a wind speed and its unit (km/h, m/s, mph or knots). The tool converts it to metres per second (km/h ÷ 3.6, mph × 0.44704, knots × 0.514444) and places it among the Beaufort class boundaries, which are set in m/s: 0.5, 1.6, 3.4, 5.5, 8.0, 10.8, 13.9, 17.2, 20.8, 24.5, 28.5 and 32.7. A speed below the first limit is force 0, and anything at or above 32.7 m/s is force 12.

The speed must not be negative. The Beaufort number and its name (for example 'Strong breeze') come from the class the converted speed falls in; the converted m/s value is shown too. The scale is defined for a standard measurement height and a steady (sustained) wind, not for gusts. If the unit is unrecognised, the tool assumes km/h.

Worked example

A forecast gives wind of 40 km/h. Converting: 40 ÷ 3.6 = 11.11 m/s. That lies between the limits 10.8 and 13.9, so it is Beaufort force 6, described as Strong breeze. If the speed were 38 km/h (10.56 m/s) it would fall just below 10.8 and be force 5, a fresh breeze.

Try this example →

Common mistakes

  • Leaving the unit on km/h while entering knots or mph. A 40-knot wind is nearly 74 km/h, not 40.
  • Entering a gust speed. Beaufort describes sustained wind, so a gust figure overstates the force.
  • Treating the Beaufort number as a speed. It is a class from 0 to 12, and each class covers a range of speeds.
  • Expecting a force above 12. All winds at or above 32.7 m/s are shown as 12, however strong.
  • Entering wind as a negative value or a direction; the field takes a speed of zero or more.

About this calculator

This calculator converts a wind speed into its Beaufort scale number and description, an empirical scale developed by Sir Francis Beaufort in 1805 that ranges from 0 (calm, smoke rises vertically) to 12 (hurricane force, widespread damage), originally based on observed effects on sailing ships and later extended to effects on land such as swaying trees and difficulty walking.

Meteorologists, sailors, and coast guard services still use Beaufort numbers in marine and weather forecasts because they translate an abstract speed into an intuitive, observable description of sea and land conditions. Enter a wind speed (in km/h, mph, or knots) to get its Beaufort force number, name (like "fresh breeze" or "gale"), and typical observed effects.

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