Use this sailing calculation for planning or education when the vessel, units, reference directions, environmental conditions, and assumptions are explicitly known.

P (ft)

Required number in ft. Luff length along the mast (P dimension).

E (ft)

Required number in ft. Foot length along the boom (E dimension).

The cited overview of Sailing supplies background for the terminology and domain context used by this tool.^[1]

Compute the triangular mainsail area from the luff (P) and foot (E) measurements. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Sail area (ft²)

Returned number in ft². Triangular sail area.

• Vessel design and loading, sea state, wind, current, tide datum, weather, chart accuracy, equipment, crew, and safety margins can make real conditions differ from a simplified result.
• Use finite inputs in the displayed units, preserve source measurements and assumptions, and independently verify consequential decisions.

Cross-check current charts, tide and weather services, instrument data, vessel manuals, and applicable navigation rules, and retain a conservative alternative plan.

• Mainsail Area Calculator

  Compute the triangular mainsail area using mainsailAreaM2 = 0.5 * luffLengthMeters * footLengthMeters.

• Roach Area Calculator

  Estimate the mainsail roach area as roachAreaM2 = 0.5 * luffLengthMeters * footLengthMeters * roachPercentage / 100 of the triangular sail area.

• Reef Percentage Calculator

  Compute the percentage of sail area reduced when sailing on a reefed headsail or mainsail.