Why is the formula 0.5 × base × height?

A triangular sail is geometrically a triangle. The area of any triangle is half the base multiplied by the perpendicular height, giving Area = 0.5 × foot × luff.

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 work for non-triangular sails like a square-top main?

No. A square-top or roach-heavy sail has extra area above the straight triangle. For those sails use the sailmaker's measured area or add a roach correction factor (typically 5–15% extra).

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

Name: Sail Area Calculator
Availability: InStock
Author: Nham Vu

Enter the base (foot) and height (luff) of your triangular sail to instantly calculate its area in square feet or square meters.

Sail Dimensions

Sail Type

Units

Foot (base) ft

Bottom edge: tack to clew

Luff (height) ft

Leading edge: tack to head

Current Sail

Enter foot and luff dimensions to calculate area.

Sail Plan

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

Summary

Enter the base (foot) and height (luff) of your triangular sail to instantly calculate its area in square feet or square meters.

How it works

Select the sail type (mainsail, jib, or spinnaker) from the dropdown.
Enter the foot (base) length — the horizontal dimension along the boom or tack-to-clew distance.
Enter the luff (height) — the vertical or leading-edge dimension from tack to head.
Choose feet or meters as your unit.
The area is computed instantly as 0.5 × foot × luff.
Add multiple sails to see the combined sail area for your full sail plan.

Use cases

Estimate the driving power of a sail plan when shopping for a used boat.
Calculate sail area-to-displacement ratio for performance comparisons.
Determine replacement sail dimensions when ordering from a sailmaker.
Compare a sloop's upwind sail area (main + jib) against a similar boat.
Check whether a proposed sail plan is balanced for light or heavy air.
Plan a reefing strategy by seeing how much area is removed at each reef.
Quickly convert between square feet and square meters for sail specs.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu