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Beaufort scale simulator

See how wind changes the sea. Explore all 13 Beaufort forces, compare wind speeds and learn to read waves, whitecaps and coastal clues.

Guide: Beaufort scale simulator

Beaufort scale chart: forces 0–12

Read across each row to connect a wind-speed range with typical sea observations. These clues support an estimate; no single clue measures the wind.

Beaufort scale chart: forces 0–12
ForceDescriptionknkm/hmphm/sWave height (m)Sea clues
0Calm<1<1<1<0.30Smooth water with almost no wind-made texture.
1Light air1–31–51–30.3–1.50.1Fine ripples appear; their tops carry no foam.
2Light breeze4–66–114–71.6–3.30.2Short, distinct wavelets remain mostly unbroken.
3Gentle breeze7–1012–198–123.4–5.40.6Some crests break, leaving occasional whitecaps.
4Moderate breeze11–1620–2813–185.5–7.91Small waves build and whitecaps become frequent.
5Fresh breeze17–2129–3819–248–10.72Longer waves develop with many white crests.
6Strong breeze22–2739–4925–3110.8–13.83Larger waves carry broad patches of breaking foam.
7Near gale28–3350–6132–3813.9–17.14Breaking foam starts to trail downwind in streaks.
8Gale34–4062–7439–4617.2–20.75.5Longer, higher waves shed spray from their crests.
9Strong gale41–4775–8847–5420.8–24.47Heavy breaking crests and spray can obscure the view.
10Storm48–5589–10255–6324.5–28.49Very high breakers spread large areas of white foam.
11Violent storm56–63103–11764–7328.5–32.611.5Exceptional waves and widespread spray restrict visibility.
12Hurricane force≥64≥118≥74≥32.714+Airborne spray and foam can severely obscure the sea.

Reference values for well-developed wind waves in the open sea. Actual waves depend on fetch, duration, depth, currents and swell.

Read the report: mean wind, gusts and swell

Fictional coastal report for practice. Wind is measured at 10 m. A long swell also arrives from a distant storm. Use the reference table, then check your reasoning below.

Mean over 10 minutes
19 kn
Highest 3-second gust
30 kn

Which Beaufort force describes the prevailing wind: 5 or 7? Can you also conclude that the waves are 2 m high?

Check the answer and the wave-height trap

Force 5. The mean of 19 kn lies in the 17–21 kn band. The 30 kn gust lies in the 28–33 kn speed band associated with force 7, but that lookup does not turn the mean wind into force 7. Keep the gust reading separate.

This exercise states the averaging periods explicitly, following the Met Office convention. Other products can use different periods. Check the provider's definition before comparing two wind reports.

The wave height is not established by these wind readings. The table's 2 m at force 5 is a reference for well-developed open-sea wind waves. Swell and local wind waves can coexist; read their height, period and direction separately. This report alone cannot establish conditions for a particular vessel or passage.

Understanding the Beaufort wind scale

What does the Beaufort scale measure?

The Beaufort scale describes wind force using numbered categories from 0, calm, to 12, hurricane force. Each category corresponds to a wind-speed band and recognisable effects. It offers a shared vocabulary for marine forecasts and observations: saying force 5 communicates more than simply saying it is windy.

A Beaufort number describes wind, not a measured wave height. When reading a forecast, distinguish the reported wind from gusts, which are brief increases. Check the forecast provider’s averaging convention, area and valid time. A momentary gust should not replace the sustained or mean wind when describing the prevailing force.

How to read Beaufort in knots, km/h, mph and m/s

Select a force, then change units to read the same category in knots, kilometres per hour, miles per hour or metres per second. For example, force 5 corresponds to the published bands 17–21 knots and 29–38 km/h. These conventional rounded bands need not have endpoints that match an exact conversion.

For a measured speed, one knot is exactly 1.852 km/h, about 1.151 mph or 0.5144 m/s. Keep the original precision until the final calculation. A Beaufort chart groups speeds into categories; changing the displayed unit does not make the wind stronger or weaker.

Beaufort and Douglas: wind force versus sea state

The Douglas scale describes sea state through wave-height classes; Beaufort describes wind force. Their numbers are not interchangeable. Force 5 and Douglas 5 mean different things, so always name the scale when recording a number. Read wind and wave information separately in a marine forecast.

The wave figures here refer to well-developed wind waves in open water. Waves need time and an uninterrupted distance of water, called fetch, to grow. Swell from distant weather, opposing currents and shallow water can change the scene. A sheltered bay and an exposed passage may look different under the same wind. Whether a wave comes onto the deck also depends on the vessel’s freeboard, heading and motion; the tanker’s motion here is an illustrative example.

Estimate wind from several clues

First separate small ripples from breaking crests, then look for how often whitecaps occur and whether foam streams downwind. On shore, compare flags, leaves and branches. Observe over time and across an exposed area: a single sheltered tree or one breaking wave gives an incomplete picture.

Use these clues as an estimate and compare them with a representative wind observation. Buildings, headlands and terrain alter local airflow. The simulator exaggerates some movement for learning and does not calculate local turbulence, storm surge or structural damage. Cloud type is not assigned by Beaufort force.

Why sailors still use Beaufort

The Met Office archive documents Francis Beaufort recording a wind scale in 1806 while commanding HMS Woolwich. He wanted more consistent logbook observations. Later versions connected force with effects on sailing vessels, making the descriptions practical for crews sharing conditions at sea.

Modern wind instruments provide numerical measurements, but the scale remains a useful reading and communication tool. Learn the progression of effects alongside the numbers. Recognising the change from isolated whitecaps to persistent foam is more useful than memorising a dramatic picture without its context.

Practise with the 3D Beaufort simulator

Start at calm and move one step at a time. Pause at forces 3, 5 and 7 to compare breaking crests and foam. Switch between the view from outside the ship and the deck view while keeping the force fixed. Then choose a speed band in the table and predict its description before reading across.

For real passage planning, combine the current official marine forecast and warnings with tides, currents, route exposure and the capabilities of the vessel and crew. This simulator builds vocabulary and observation skills; it does not decide whether a voyage is safe or reproduce a particular location’s weather.

Beaufort scale questions

How windy is Beaufort force 5?

Force 5 is a fresh breeze: 17–21 knots, conventionally 29–38 km/h. Frequent whitecaps and swaying small trees are typical clues. The indicative open-sea wave height is about 2 metres, not a prediction for your location.

At what Beaufort force does a gale begin?

Force 8 is gale, with a band of 34–40 knots or 62–74 km/h. Force 7 is near gale. Warning criteria and wording depend on the issuing service, so read the actual marine warning.

Does force 12 mean a tropical hurricane?

No. Hurricane force describes wind of 64 knots or more in this scale. It does not identify a tropical cyclone or give a Saffir–Simpson category; other kinds of storms can produce hurricane-force winds.

Can I convert Beaufort directly to wave height?

There is no exact conversion. The table gives open-sea reference heights for developed wind waves. Wind duration, fetch, swell, currents and depth determine the actual waves; use the wave forecast and observations as well.

Sources and further reading

Source review

From calm to hurricane force

Animation is paused to respect your reduced-motion preference. You can still change the force and viewpoint.

An educational illustration: waves and coastal movement are simplified. This is not a forecast; a Beaufort force does not determine cloud cover or specific damage. Reference values for well-developed wind waves in the open sea. Actual waves depend on fetch, duration, depth, currents and swell.