Beaufort Wind Scale Converter

Understanding the Beaufort wind scale converter — concept and principle

The Beaufort scale describes wind strength with a number from 0 (calm) to 12 (hurricane force), linked to what you can see: smoke rising straight up, leaves rustling, whole trees swaying, or the sea turning white with foam. Devised by Francis Beaufort of the Royal Navy in the early 1800s, it is still used in marine forecasts. This converter turns a wind speed in km/h into a Beaufort number, a description and the speed in m/s and knots.

A 45 km/h wind is force 6 of 12 — a strong breeze.

How it is calculated

Convert to m/s: v(m/s) = v(km/h) ÷ 3.6
Beaufort number: B = (v ÷ 0.836)^(2/3), rounded to the nearest whole number and capped at 12
Knots: v(km/h) ÷ 1.852

The description follows the standard names: 0 Calm, 1 Light air, 2 Light breeze, 3 Gentle breeze, 4 Moderate breeze, 5 Fresh breeze, 6 Strong breeze, 7 Near gale, 8 Gale, 9 Strong gale, 10 Storm, 11 Violent storm, 12 Hurricane force.

The principle

Beaufort's original scale had no speeds at all; it was based on how a warship's sails behaved. When anemometers became common, meteorologists fitted an empirical formula linking the force numbers to measured winds at 10 m height: v = 0.836 × B^(3/2) m/s. Inverting it gives the formula above. The 3/2 power means each step covers a wider speed range than the one before, which matches how damage and sea state grow faster than wind speed. Rounding to the nearest integer reproduces the usual table limits, for example force 6 runs from about 10.8 to 13.8 m/s.

Worked example

Input: 45 km/h.
m/s: 45 ÷ 3.6 = 12.5 m/s.
B = (12.5 ÷ 0.836)^(2/3) = 14.952^(2/3) ≈ 6.07, which rounds to 6.
Description: Strong breeze.
Knots: 45 ÷ 1.852 = 24.30 kn (24.29805616).

Each point is the calculator re-run with only “Wind speed (km/h)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Wind speed (km/h)	Beaufort number
11.2	2
22.5	4
33.8	5
45	6
56.2	7
67.5	8
90	10

How to read the result

Where does your result fall?

Force 6 (39–49 km/h) moves large branches, makes umbrellas hard to use and raises large waves with white foam crests at sea; many small-craft advisories begin around force 6 or 7. Force 8 (gale, 62–74 km/h) breaks twigs off trees and makes walking difficult. Force 12 means sustained winds of at least about 118 km/h. Gusts are often well above the mean wind.

Common mistakes

Entering a gust speed instead of the sustained (mean) wind, which overstates the force.
Confusing knots with km/h: 24 kn is about 45 km/h, not 24.
Expecting Beaufort numbers above 12; extensions to 17 exist in some regions but are not part of the standard scale.

Keep in mind: Wind measured at the surface varies with height, terrain and buildings, and the scale describes typical effects, not exact thresholds for danger. For boating or outdoor activities, rely on official forecasts and warnings.

Frequently asked questions

What Beaufort number is a typhoon?

Tropical cyclones of hurricane or typhoon strength have sustained winds of force 12 by definition, but the Beaufort scale cannot distinguish their intensity; dedicated scales are used for that.

Why does the formula use m/s at 10 m height?

The standard height for wind measurement at weather stations is 10 m above open ground, so the empirical fit uses that reference.

Is the scale used on land as well as at sea?

Yes. Descriptions for land, such as smoke drift and tree movement, were added later so the scale could be estimated without instruments.

Sources: Met Office (UK), The Beaufort wind force scale

Checked 8 Nov 2026. Standard textbook formulas in SI units, computed in your browser. For learning and estimates — real designs must follow your local codes and be checked by a qualified engineer.

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