Beaufort Wind Scale & Sea State Estimator
Convert wind speed to Beaufort force, sea state description and estimated wave height.
Last reviewed by the myCalculator Editorial Team
Input Parameters
The distance the wind blows over open water without obstruction.
How long the wind has blown steadily from the same direction.
Calculation Results
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Formula & How Beaufort Wind Scale & Sea State Estimator Works
The Beaufort scale, devised by Admiral Francis Beaufort in 1805, maps wind speed to observable sea conditions rather than instrument readings. Wave height depends on three things: wind speed, fetch and duration. A gale over a short fetch produces a steep dangerous chop rather than large waves, while the same wind across an ocean fetch builds a fully developed sea. Whichever of fetch or duration runs out first limits the sea that can develop. Worked example: a 22 knot wind is 11.3 m/s, which is force 6 (strong breeze) on the Beaufort scale. For a fully developed sea the significant wave height is about 0.0248 × 11.3² = 3.2 m, but waves only reach that if the fetch and duration are long enough, so a limited fetch or short duration gives smaller waves. Significant wave height is the average of the highest third of waves, and individual waves can be nearly twice that.
- Enter Wind Speed (knots) (kts): Input your target parameter value.
- Enter Fetch — Open Water Distance (NM) (NM): Input your target parameter value.
- Enter Wind Duration (hours) (hrs): Input your target parameter value.
- Apply Formula: Calculate using
Fully Developed Hs ≈ 0.0248 × U² (U in m/s) | Fetch-limited Hs from SMB growth curves. - Review Results: View exact computed answers, metrics, and worked mathematical proofs.
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Frequently Asked Questions (FAQs)
What Beaufort force is dangerous for small boats?
Force 6 (22 to 27 knots) triggers a strong wind warning and small craft should not depart. Force 8 is a gale and hazardous for all small vessels.
Why do the same winds produce different wave heights?
Waves need fetch and time to build. Twenty-five knots across 5 NM of sheltered water produces a short steep chop, while the same wind over 500 NM of open ocean builds a fully developed sea several metres high.
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