Sail Size Calculator
The sail size calculator determines the total standard sail area of your boat based on standard rig dimensions (I, J, P, and E). Knowing your accurate sail area helps in selecting replacement sails, estimating performance ratios, and calculating handicap ratings.
Understanding Rig Dimensions (I, J, P, E)
Naval architects and sailmakers use standard alphabet designations to represent the primary rig dimensions of a sailboat. These simple triangular calculations give the 100% standard sail area, which acts as a baseline for performance ratios.
What do the letters mean?
- P (Mainsail Hoist): The vertical dimension of the mainsail, measured from the top of the boom to the highest point the sail can be hoisted on the mast.
- E (Mainsail Foot): The horizontal dimension of the mainsail along the boom, measured from the aft face of the mast to the outermost attachment point on the boom.
- I (Foretriangle Height): The vertical distance from the sheer line (deck level) to the highest forestay attachment point on the mast.
- J (Foretriangle Base): The horizontal distance from the front face of the mast to the forestay attachment point on the deck (or bowsprit).
How is it Calculated?
Because sails are essentially triangles, we use the standard area formula (Base × Height ÷ 2).
Mainsail Area: (P × E) / 2
100% Foretriangle Area: (I × J) / 2
Note: If you run a larger overlapping genoa (e.g., 135%), your actual headsail area will be larger
than the standard 100% foretriangle area calculated here.