Beaufort wind scale
Unit conversionHow strong is the wind on the Beaufort scale?
Turn a wind speed in m/s, km/h, knots or mph into its Beaufort force and name.
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Beaufort force
Force 5
Fresh breeze, 8.0–10.7 m/s
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The Beaufort scale
Mean wind speeds of each force, as in the WMO table.
| Force | Name | Wind (mph) |
|---|---|---|
| 0 | Calm | 0–0.7 |
| 1 | Light air | 0.7–3.6 |
| 2 | Light breeze | 3.6–7.6 |
| 3 | Gentle breeze | 7.6–12.3 |
| 4 | Moderate breeze | 12.3–17.9 |
| 5 | Fresh breeze | 17.9–24.2 |
| 6 | Strong breeze | 24.2–31.1 |
| 7 | Near gale | 31.1–38.5 |
| 8 | Gale | 38.5–46.5 |
| 9 | Strong gale | 46.5–54.8 |
| 10 | Storm | 54.8–63.8 |
| 11 | Violent storm | 63.8–73.1 |
| 12 | Hurricane | ≥ 73.1 |
Turn a wind speed in m/s, km/h, knots or mph into its Beaufort force and name.
How to use
- Type the wind speed from a forecast or an anemometer.
- Choose its unit: metres per second, kilometres per hour, knots or miles per hour.
- Read the Beaufort force and its name; the table shows every force, with yours marked.
How it works
The Beaufort scale sorts wind into 13 forces, from 0 (calm) to 12 (hurricane). Admiral Francis Beaufort made it in 1805 for sailors, who judged the wind by the sea and the sails. Today the World Meteorological Organization (WMO) defines each force as a range of mean wind speed, measured over ten minutes at 10 m above the ground.
The tool turns your speed into metres per second (1 knot = 1852/3600 m/s, 1 mph = 0.44704 m/s, 1 km/h = 1/3.6 m/s) and finds the force whose range holds it. For example, 10 m/s lies between 8.0 and 10.7 m/s, so it is force 5, a fresh breeze. The ranges grow with the force, roughly as v ≈ 0.836 × B^1.5 m/s, but the table, not the formula, is the definition.
The table comes from the WMO scale as published by the Icelandic Meteorological Office. Gusts are stronger than the mean wind, so a forecast's gust speed reads higher on the scale than the wind itself. Ranges in other units are converted from the m/s table, so they can differ slightly from tables printed in knots.
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Frequently asked questions
What wind speed is a gale?
Force 8, a gale, is a mean wind of 17.2–20.7 m/s, about 62–75 km/h or 34–40 knots.
Is hurricane force the same as a hurricane?
Force 12 means a mean wind of at least 32.7 m/s (about 118 km/h). A hurricane is a tropical storm that reaches that wind; the scale only measures the wind.
Why does the forecast give gusts separately?
Gusts are short peaks, often 30–50 % above the mean wind. The Beaufort scale is defined for the mean, so use the mean wind for the force.
Can I get one exact wind speed from a Beaufort number?
No. Each force covers a range of speeds. Read its lower and upper bounds in the table rather than treating it as one exact value.
Does the scale include forces above 12?
Not here. All speeds from 32.7 m/s upward are force 12. Regional extended typhoon scales are not included.
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