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.
Specialist tool for Sailing1 documented formula8 real workflowsPrivate in your browser
Use this result well
A quick decision brief for this specific tool
Inputs that matter
Luff / Height, Foot / Base, Sail Type, LP Percentage (jib)
Output to expect
Sail Area Calculator
How it works
1 documented formula across 1 calculation mode
- Keep 3 bounded inputs within the limits shown beside the fields.
- Confirm that every value uses the unit and time basis shown before comparing scenarios.
- Change one input at a time to see which assumption materially changes the result.
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Reference & details
How it works
Updated July 2026
How it works
Updated July 2026Triangular Sail Area
A simple jib or mainsail without roach approximates a triangle: half the base times height (luff).
Area = (foot × luff) / 2Mainsail 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
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.