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Beaufort scale
A 0–12 wind-force scale based on observed sea or land effects, devised by Admiral Beaufort in 1805.
Also known as: Bft, beaufort
The Beaufort scale classifies wind by what it does, not by what an anemometer measures. Force 0 is calm, force 6 is a strong breeze (whitecaps everywhere, hard to use an umbrella), force 8 is a gale (twigs break off trees), force 12 is a hurricane.
Wind sports reference points:
- Bft 3 (7–10 kt) — light wind, foil / big gear
- Bft 4 (11–16 kt) — comfortable for most riders
- Bft 5 (17–21 kt) — fully powered freestyle / wave conditions
- Bft 6 (22–27 kt) — small gear, big waves, experienced only
- Bft 7+ (28+ kt) — storm session territory
Marine forecasts and harbour warnings still use Beaufort, so it’s worth recognising even if you check raw knots on your app.
Related reading: Types of Wind, Kite Size from Forecast.
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Related terms
- Knots The wind-speed unit used across sailing, aviation and weather — 1 knot = 1 nautical mile per hour ≈ 1.852 km/h.
- Gust A short, sharp increase in wind speed lasting seconds, well above the average.
- Gust factor The ratio of peak gust to average wind — the single most useful number for telling smooth wind from a fight.