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.

Mainsail area (m²)

Required number in m². Rated area of the mainsail.

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

Compute the mainsail aspect ratio as aspectRatio = luffLengthMeters^2 / mainsailAreaM2; taller narrower sails have higher ratios. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Aspect ratio

Returned number. Aspect ratio of the mainsail planform.

• 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.
• Luff length P must be at least 0.
• Mainsail area must be at least 0.
• 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.

• Keel Aspect Ratio

  Compute the keel aspect ratio as keelAspectRatio = draftMeters^2 / keelAreaM2; deep fin keels have high ratios.

• Mainsail Area Calculator

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

• Jib Aspect Ratio

  Compute the jib aspect ratio as aspectRatio = iMeasurementMeters^2 / jibAreaM2 using the forestay height I and the measured jib area.