Enter a wind speed in mph, km/h, knots, m/s or ft/s to get its Beaufort force from 0 (calm) to 12 (hurricane force), with what the sea and land look like and typical wave height. Or pick a force number to see its speed range in every unit.
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How to use the Beaufort Scale Converter
Choose the direction: wind speed to Beaufort, or Beaufort force to wind speed.
Type the speed and pick its unit (mph, km/h, knots, m/s or ft/s), or select a force number.
Read the force and its name, such as Force 5, Fresh breeze.
Check the sea and land descriptions and the typical wave height.
Use the color chart and table to compare with neighbouring forces or download the scale.
Beaufort scale formula
The modern scale is defined by speed bands in knots (WMO). A simple empirical relation links the force number B to the mean wind speed v measured 10 m above the surface:
v = 0.836 × B3/2 m/s and inversely B = (v ÷ 0.836)2/3
For example, 10 m/s gives B = (10 ÷ 0.836)2/3 ≈ 5.2, which is Force 5. The converter uses the official knot bands for the force number and shows the formula value as a decimal so you can see when a wind is near the top or bottom of its band.
Sailing and outdoor guide by force
Force
Knots
What it means in practice
0–2
0–6
Light winds: sailing is slow, kites struggle, perfect for paddling and drone flights.
3–4
7–16
Ideal sailing and kite flying; whitecaps start to appear around Force 4.
5
17–21
Experienced small-boat sailors reef; beginners should stay ashore. Most consumer drones reach their limit.
6–7
22–33
Small craft advisories are common; cycling into the wind is hard; outdoor events secure tents.
8–9
34–47
Gale warnings; falling branches and loose objects become a hazard; avoid coastal walks and ferries may stop.
10–12
48+
Storm to hurricane force: structural damage, power cuts and dangerous seas. Follow official warnings.
Measuring wind without an anemometer
The Beaufort scale was designed for estimating wind by eye, and it still works: look at smoke, leaves, flags and branches on land, or at ripples, whitecaps and foam streaks on water, and match them to the descriptions in the table. A cheap handheld anemometer held at arm's length gives a reading closer to the ground than the standard 10 m height, so it will usually read lower than the official forecast.
Frequently asked questions
What is the Beaufort scale?
It is a 0 to 12 scale of wind force devised by Admiral Francis Beaufort in 1805 and later tied to measured speeds. Each number describes a speed band and its visible effects, from Force 0 (calm, smoke rises straight up) to Force 12 (hurricane force, 64 knots or more).
How do you convert wind speed to Beaufort?
Convert the speed to knots, round it, and find its band: 1–3 kn is Force 1, 4–6 Force 2, 7–10 Force 3, 11–16 Force 4, 17–21 Force 5, 22–27 Force 6, 28–33 Force 7, 34–40 Force 8, 41–47 Force 9, 48–55 Force 10, 56–63 Force 11 and 64+ Force 12. The empirical formula v = 0.836 × B^1.5 m/s gives a continuous estimate.
How fast is a Force 6 wind?
Force 6, a strong breeze, is 22–27 knots, which is 25–31 mph, 39–49 km/h or 10.8–13.8 m/s. Large branches move, wires whistle and umbrellas become hard to use; at sea, large waves with extensive whitecaps form.
What Beaufort number is a gale?
Force 8 is a gale (34–40 knots, 39–46 mph), Force 9 a strong or severe gale (41–47 knots), Force 10 a storm (48–55 knots) and Force 11 a violent storm (56–63 knots). Gale warnings are issued from Force 8.
Is the Beaufort scale based on sustained wind or gusts?
On sustained (mean) wind, normally averaged over 10 minutes at 10 m above the surface. Gusts can be 30–50% stronger than the mean, so a Force 6 day may bring gusts that feel like Force 8.
Are the wave heights exact?
No. The listed heights are probable values in the open sea well away from land, after the wind has blown long enough. Waves are smaller in sheltered water or with a short fetch, and swell from distant storms can make them larger.
Does the Beaufort scale go above 12?
The standard WMO scale ends at 12. Some countries, such as China and Taiwan, use extended forces 13 to 17 for typhoons. For hurricanes, the Saffir–Simpson scale is used instead, starting at 74 mph sustained wind.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.