Beaufort wind scale calculator
Convert wind speed to the Beaufort force (0 to 12) and see what each level means.
The Beaufort scale rates wind from 0 (calm) to 12 (hurricane) by observable effects, widely used in sailing and weather.
How the calculation works
Created by Francis Beaufort in 1805, the scale ties wind-speed ranges to a force number from 0 to 12 and, crucially, to the observable effect on sea and land. It was designed for an era with no anemometer aboard ship, and it survived because it remains the most practical way to estimate wind without an instrument.
The full scale
| Force | Description | Speed | What you see on land |
|---|---|---|---|
| 0 | Calm | < 1 mph | smoke rises vertically |
| 1–2 | Light air / light breeze | 1–7 mph | leaves barely move |
| 3–4 | Gentle / moderate breeze | 8–18 mph | flags flap, dust lifts |
| 5–6 | Fresh / strong breeze | 19–31 mph | large branches sway; umbrellas invert |
| 7–8 | Near gale / gale | 32–46 mph | hard to walk against; twigs break off |
| 9–10 | Strong gale / storm | 47–63 mph | structural damage; trees uprooted |
| 11–12 | Violent storm / hurricane | 64 mph and above | widespread devastation |
Why the scale is still used
Because it converts an abstract number into a decision. "25 mph" means little to most people; "large branches swaying and umbrellas turning inside out" is immediately actionable — for sailing, flying a drone, working at height or securing loose objects.
Gusts are what cause damage
Beaufort describes sustained wind. Gusts routinely reach 1.5 times the sustained speed, and it is the gust, not the average, that removes roof tiles and topples trees. A forecast of force 7 sustained can carry gusts well into force 9 territory.
Examples
- Wind of 25 km/h: force 4 ("moderate breeze", raises dust and paper).
- Wind of 90 km/h: force 10 ("storm", trees uprooted).
Frequently asked questions
At what force is it a hurricane?
Force 12, when wind exceeds ~118 km/h. Above that the classic Beaufort scale ends.
What is the Beaufort scale used for today?
It is still used in sailing and marine forecasts, and to describe wind by its observable effects without an anemometer.
How does it differ from the hurricane scale?
Beaufort goes 0–12 and covers all winds; the Saffir-Simpson scale (categories 1–5) classifies only hurricanes, above 118 km/h.
At what speed does wind get dangerous?
At 50–74 km/h walking against it is hard; 75–102 km/h dislodges roof tiles and fells trees; above 103 km/h damage is widespread.
Is 100 km/h wind twice as strong as 50?
No, four times stronger. Wind pressure grows with the square of speed.
Sustained wind or gusts?
Gusts, when assessing risk. They can exceed the sustained average by 30–50% and cause most of the damage.
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See all →Updated on June 30, 2026 · by Rafael Rossi · Methodology & sources