Sail Area Calculator

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