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Gust factor
The ratio of peak gust to average wind — the single most useful number for telling smooth wind from a fight.
Also known as: G-factor, gust ratio
Gust factor is gust ÷ average over the same time window. 15 kt gusting 18 has a factor of 1.2 — smooth. 15 kt gusting 25 is a factor of 1.67 — a different sport.
Rider rules of thumb:
- Under 1.3 — clean, size for the average
- 1.3–1.5 — gusty, size for the gust, not the average
- Over 1.5 — unstable; pack down a size and stay close to the beach
Gust factor also tells you what kind of wind you’re getting before you check anything else:
- ~1.1 — clean sea breeze, open-ocean trades
- 1.3–1.4 — post-frontal westerlies, Mistral in the open
- 1.5+ — gusty offshore, collapsing thermal, Bora, Föhn descent, lee of an island
A forecast number with no gust factor is half the story. Pair it with the Kite Size from Forecast sizing matrix to convert it into the right kite on the beach.
Related terms
- Gust A short, sharp increase in wind speed lasting seconds, well above the average.
- Lull A temporary drop in wind speed below the running average — the opposite of a gust.
- Beaufort scale A 0–12 wind-force scale based on observed sea or land effects, devised by Admiral Beaufort in 1805.
- Sea breeze A daytime onshore wind driven by uneven heating of land and water — the engine of most summer coastal sessions.
- Föhn wind A warm, dry, often gusty downslope wind on the lee side of a mountain range — Föhn in the Alps, Chinook in the Rockies, Halny in the Tatras.