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Sailing & Marine Calculator

Sail Area Calculator. Calculate sail area from luff, leech, and foot measurements for different sail types. Estimate mainsail and headsail area for sailing performance.

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Inputs that matter
Luff / Height, Foot / Base, Sail Type, LP Percentage (jib)
Output to expect
Sail Area Calculator
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Triangular Sail Area

A simple jib or mainsail without roach approximates a triangle: half the base times height (luff).

Area = (foot × luff) / 2

Mainsail with Roach

Modern mainsails have roach extending beyond the straight leech. Add roach area using the roach percentage or measure the leech curve.

Total mainsail area ≈ (P × E / 2) × (1 + roach% / 100)

Genoa LP Ratio

Genoa area scales with LP (luff perpendicular) as a percentage of J dimension. A 150% genoa has LP = 1.5 × J.

Genoa area ≈ (LP × I) / 2 (LP in % of J × J)

Updated: July 2026

Example Scenarios

P (luff) 38 ft, E (foot) 13 ft: area = 38 × 13 / 2 = 247 sq ft. With 8% roach: ~267 sq ft total mainsail area.

I (foretriangle height) 42 ft, J (base) 12 ft: 100% jib area = 12 × 42 / 2 = 252 sq ft. Total working sail area ~519 sq ft.

LP = 18 ft (150% of J=12), I = 42 ft: genoa area = 18 × 42 / 2 = 378 sq ft. Significantly more drive in light winds than 100% jib.

Common Mistakes to Avoid

Using boom length instead of E measurement for mainsail foot

E is the mainsail foot dimension, not always full boom length. Loose-foot mainsails and short-footed racing mains have E less than boom length.

Ignoring roach on modern mainsails

Roach adds 5–15% area beyond the triangle approximation. Rating rules and sail balance calculations need roach included for accuracy.

FAQ

P (luff length along mast) and E (foot length along boom) from the sail specification or measurement diagram. Add roach correction for accurate modern mainsail area.

Percentage is LP (luff perpendicular) as a fraction of J (foretriangle base). A 130% genoa extends 30% beyond the mast when sheeted — more area for light air.

Yes. Larger sail area relative to boat length generally means faster potential speed and a lower (faster) PHRF handicap. Accurate area is needed for rating certificates.

Lay sail flat, measure luff, leech, and foot. For triangulated sails use (luff × foot) / 2. Include roach by measuring maximum width perpendicular to luff.

I is foretriangle height (deck to masthead for headsail calculations). P is mainsail luff length (boom to masthead or headboard). They differ when mainsail is shorter than mast.

About Sail Area Calculator

Sail area drives boat speed and balance. This calculator computes sail area in square feet or square meters from luff, leech, foot, and roach measurements for mainsails, jibs, genoas, and spinnakers.