Sail Area Calculator
Calculate total sail area for a sloop rig (mainsail + jib).
Compute sail area-to-displacement ratio to assess boat performance.
How Sail Area Is Calculated
Total sail area determines how much wind power a boat can capture. The main driving sails — mainsail and headsail (jib or genoa) — are each calculated separately using their geometry.
Triangular Sail Area:
Area = 0.5 × Base × Height
For a mainsail: Base = foot length (boom), Height = luff length (mast to boom attachment) For a jib/genoa: Base = LP (perpendicular from clew to forestay), Height = luff length
Sail Area to Displacement Ratio (SA/D):
SA/D = Total Sail Area (ft²) / (Displacement in lbs / 64)^(2/3)
Higher SA/D = more performance-oriented.
Worked Example: A 35-foot sloop:
- Mainsail: foot = 12 ft, luff = 38 ft → Area = 0.5 × 12 × 38 = 228 ft²
- 110% Genoa: LP = 14 ft, luff = 34 ft → Area = 0.5 × 14 × 34 = 238 ft²
- Total Sail Area = 466 ft²
Displacement = 14,000 lbs:
- SA/D = 466 / (14,000/64)^(2/3) = 466 / (218.75)^(2/3) = 466 / 36.2 = 12.9
SA/D Reference Values:
- Under 14: heavy cruiser, comfortable but slow
- 14–18: cruiser-racer, balanced
- 18–22: performance cruiser
- Over 22: racing yacht, requires skill in heavy air
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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