Weather / Wind
Beaufort Scale Converter
Convert a wind speed in km/h, m/s, knots, or mph to its Beaufort force, with the description and what it looks like at sea and on land, plus the full table.
Beaufort Scale Converter: The Beaufort scale sorts mean wind speeds, measured 10 m above the ground, into forces 0 (calm) to 12 (hurricane force). The speed limits in knots, m/s, and km/h follow the World Meteorological Organization's table, and each force comes with its standard signs at sea and on land. A wind of 25 km/h is force 4, a moderate breeze. Runs 100% locally in your browser with zero server file uploads.
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Force 4 · Moderate breeze
Dust and loose paper lifted; small branches move. Small waves, fairly frequent white horses.
| Force | Description | km/h | knots | m/s |
|---|---|---|---|---|
| 0 | Calm | < 1 | < 1 | < 0.3 |
| 1 | Light air | 1–5 | 1–3 | 0.3–1.5 |
| 2 | Light breeze | 6–11 | 4–6 | 1.6–3.3 |
| 3 | Gentle breeze | 12–19 | 7–10 | 3.4–5.4 |
| 4 | Moderate breeze | 20–28 | 11–16 | 5.5–7.9 |
| 5 | Fresh breeze | 29–38 | 17–21 | 8–10.7 |
| 6 | Strong breeze | 39–49 | 22–27 | 10.8–13.8 |
| 7 | Near gale | 50–61 | 28–33 | 13.9–17.1 |
| 8 | Gale | 62–74 | 34–40 | 17.2–20.7 |
| 9 | Strong gale | 75–88 | 41–47 | 20.8–24.4 |
| 10 | Storm | 89–102 | 48–55 | 24.5–28.4 |
| 11 | Violent storm | 103–117 | 56–63 | 28.5–32.6 |
| 12 | Hurricane force | 118+ | 64+ | 32.7+ |
The scale follows the World Meteorological Organization's table of mean wind speeds at 10 m above the ground; gusts can be much stronger.
Reading the wind without an instrument
On land, the scale's signs let you estimate the wind by eye: smoke drifting at force 1, leaves rustling at force 2, small branches moving at force 4, whole trees swaying at force 7. At sea, white horses appear at force 3 or 4 and streaks of foam at force 8.
To convert between speed units, use knots to km/h or mph to km/h; for how cold the wind makes it feel, the wind chill calculator.
Warnings and the scale
Marine forecasts use the scale directly: in the UK, a gale warning is issued for force 8 or more, and small-craft advisories in many countries start around force 6. Land forecasts usually give speeds in km/h or mph with separate gusts.
How to use it
- Enter a wind speed and choose its unit.
- Read the Beaufort force and its description.
- Use the table to compare the speeds for each force in every unit.
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Frequently asked questions
Who made the Beaufort scale?
Francis Beaufort, a British naval officer, devised it in 1805 to describe wind by its effect on a ship's sails; descriptions of the sea and land were added later, and speeds were fixed in the 20th century.
Does the scale include gusts?
No: it describes the mean wind over 10 minutes. Gusts are often 30–50% stronger, so weather forecasts list them separately.
Is there a force 13 or higher?
Some countries, such as China and Taiwan, extend the scale to force 17 for typhoons, but the international scale stops at 12.
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