Why is the formula 0.5 × dimension 1 × dimension 2?

A triangle is half the product of a base and its perpendicular height. That means the dimension pair matters: P and E for a nominal mainsail rig triangle, luff and LP for a triangular headsail, and I and J for a foretriangle. Two edge lengths that are not perpendicular cannot be substituted.

What is the "foot" of a sail?

The foot is the bottom edge of the sail, stretching from the tack (lower front corner) to the clew (lower rear corner). On a mainsail it runs along the boom.

What is the "luff" of a sail?

The luff is the leading (forward) edge of the sail, running from the tack (bottom) up to the head (top). On a mainsail it runs up the mast; on a jib it follows the forestay.

Does this give certified or measured sail area?

No. This gives nominal triangular area. World Sailing measurement definitions include widths and luff perpendicular, while rating systems such as ORC use girths and other measurements for curved sails. Use the applicable class or rating rule and an official measurer for certification.

What is a typical sail area-to-displacement ratio?

Most cruising monohulls fall between 16 and 20 (imperial, with displacement in cubic feet). Performance boats exceed 20; heavy cruisers may be below 16. Higher ratios mean more power in light air.

Can I add the mainsail and jib areas together?

Yes. Total upwind sail area is simply the sum of all sails you are flying simultaneously. Use the "Add Sail" feature to accumulate multiple sails.

Sail Area Calculator

Choose the measurement method: mainsail P × E, headsail luff × LP, foretriangle I × J, or base × perpendicular height; nominal area is half the product.

Sail Dimensions

Sail Type

Units

P (mainsail hoist) ft

Maximum mainsail luff/hoist dimension on the mast.

E (mainsail foot limit) ft

Maximum mainsail foot dimension along the boom.

Current Sail

Enter the two dimensions defined by the selected method.

Sail Plan

No sails added yet. Use "Add to Sail Plan" above.

Nominal triangle, not certified measured area

The two entered dimensions must be perpendicular as defined by the selected method. Roach, square tops, girths and curved edges are outside this estimate. For rating or class compliance, use the applicable measurement rule and an official measurer. Measurement terminology: World Sailing Equipment Rules; measured-area context: ORC sail measurements.

Summary

Choose the measurement method: mainsail P × E, headsail luff × LP, foretriangle I × J, or base × perpendicular height; nominal area is half the product.

How it works

Select the measurement method that matches the dimensions you have.
For a mainsail rig triangle, enter P (mainsail hoist) and E (mainsail foot limit).
For a headsail, enter luff length and LP; for a foretriangle, enter I and J.
Choose feet or meters as your unit.
Perpendicular-pair modes use 0.5 × dimension 1 × dimension 2; the three-side mode uses Heron's formula.
Add multiple sails to see the combined sail area for your full sail plan.

Use cases

Estimate nominal mainsail area from published P and E rig dimensions.
Estimate headsail area from luff length and luff perpendicular (LP).
Calculate the nominal foretriangle area from I and J dimensions.
Add compatible nominal areas for a quick sail-plan comparison.
Quickly convert between square feet and square meters for sail specs.

Frequently Asked Questions

Last updated: 2026-09-19 · Reviewed by Nham Vu