Beaufort Scale Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/5/2026
The Beaufort scale classifies wind strength from 0 (calm) to 12 (hurricane) based on its speed in km/h. A 45 km/h wind corresponds to force 6, described as a "strong breeze."
Explanation
The Beaufort scale, developed in the early 19th century to estimate wind strength from its observable effects (sea state, movement of trees, property damage) before reliable measuring instruments existed, remains today the international reference for qualitatively describing wind strength, officially adopted by the World Meteorological Organization in 1874. Each degree, from 0 (dead calm) to 12 (hurricane), corresponds to a speed range in km/h and a description characteristic of its effects. Weather services rely on this scale in their high-wind advisories: wind is generally considered dangerous starting at force 7 (near gale, 50 km/h), with significant risks to light structures, trees, and traffic from force 9 (75 km/h) onward. This scale remains used in both maritime navigation and everyday land-based meteorology, notably to communicate wind intensity intuitively, without having to interpret a raw km/h figure.
Example: a 45 km/h wind
Inputs
Wind speed: 45 km/h.
Calculation
45 km/h falls within the 39-49 km/h range of the Beaufort scale, which corresponds to force 6, described as a "strong breeze."
Result
A 45 km/h wind corresponds to force 6 on the Beaufort scale (strong breeze).
Frequently asked questions
At what force does wind become dangerous?
Wind is generally considered dangerous starting at force 7 (near gale, 50 to 61 km/h), with increased risks to light structures, trees, and vehicles from force 9 (75 to 88 km/h) onward. Weather services use these thresholds as benchmarks in their weather advisories.
Does the Beaufort scale apply to gusts or to average wind?
The Beaufort scale was designed to describe sustained average wind, not instantaneous gusts, which are generally stronger and briefer. A 100 km/h gust can therefore occur alongside an average wind corresponding to a lower Beaufort force than the gust alone would suggest.
Why does this scale only have 13 degrees?
Because it was originally designed to cover the full range of wind conditions encountered at sea, from dead calm to hurricane. Beyond force 12, there's no additional Beaufort degree: hurricane-force winds are instead classified by other, more specific scales, such as the Saffir-Simpson scale for tropical cyclones.