Sail Area Calculator

Every Sail Reduces to Triangles

Regardless of a sailboat's rig complexity, its sail area comes down to triangle geometry — base times height, halved. This calculator offers a simple triangle mode for a single sail, and a sloop-rig mode that adds the mainsail's area to the foretriangle (headsail) area using the standard "I, J, P, E" rig-dimension convention sailmakers and class associations use.

The Formulas

Simple Triangle: Area = 0.5 × Base × Height

Sloop Rig:
Mainsail Area = 0.5 × P × E
Foretriangle Area = 0.5 × I × J
Total Sail Area = Mainsail + Foretriangle

P is the mainsail luff (leading edge) length, E is the mainsail foot length, I is the foretriangle height (mast to forestay attachment), and J is the foretriangle base (mast to headstay along the deck).

Worked Examples

Both calculation modes
Mode	Inputs	Result
Simple Triangle	Base 12 ft, height 30 ft	180.00 sq ft
Sloop Rig	P = 32 ft, E = 12 ft, I = 38 ft, J = 13 ft	Mainsail 192.00 + Foretriangle 247.00 = 439.00 sq ft

Where This Matters

Sail selection and sizing — total sail area is a key input to sail-area-to-displacement ratio, a standard measure of how powered-up (or conservative) a given boat's rig is.
Handicap racing — rig dimensions like I, J, P, and E feed directly into common racing handicap and rating systems.
Custom or replacement sail quotes — sailmakers use these same triangle calculations as the starting point for estimating material and cost on a new sail.

How to Use This Calculator

Choose the mode: Simple Triangle Sail or Sloop Rig (Main + Jib).
For Simple Triangle: enter Base (ft) and Height (ft).
For Sloop Rig: enter Mainsail Luff Length P, Mainsail Foot Length E, Foretriangle Height I, and Foretriangle Base J (all in feet).
Select Calculate to see the sail area or areas.

Related Calculations

Estimate the resulting hull speed with the Displacement Hull Speed Calculator, or check draft under sail with the Boat Draft Calculator.