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

I measurement (m)

Required number in m.

J measurement (m)

Required number in m.

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

Calculate the triangular jib area from the I and J mast and deck measurements. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Jib area (m²)

Returned number in m².

• 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.

• Sail Area Calculator

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

• Roach Area Calculator

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

• Mainsail Area Calculator

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