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

Luff length P (m)

Required number in m. Luff length P along the mast.

Foot length E (m)

Required number in m. Foot length E along the boom.

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

Compute the triangular mainsail area using mainsailAreaM2 = 0.5 * luffLengthMeters * footLengthMeters. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Mainsail area (m2)

Returned number in m2. Area of the triangular mainsail.

• 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.

• Roach Area Calculator

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

• Sail Area Calculator

  Compute the triangular mainsail area from the luff (P) and foot (E) measurements.

• Main Aspect Ratio

  Compute the mainsail aspect ratio as aspectRatio = luffLengthMeters^2 / mainsailAreaM2; taller narrower sails have higher ratios.