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

Sail area (ft²)

Required number in ft². Total upwind sail area.

Displacement (lb)

Required number in lb. Displacement in pounds (seawater).

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

Compute the sail area to displacement ratio; above fifteen indicates good light-air performance. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

SA/D

Returned number. SA/D ratio; fourteen to seventeen is typical for cruisers.

• 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.

• Displacement Length Ratio Calculator

  Compute the displacement-to-length ratio; below two hundred is light, above three hundred is heavy.

• Jib Aspect Ratio

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

• Wind Pressure on Sail Calculator

  Compute aerodynamic force on a sail from dynamic pressure using 0.5 times air density times wind speed squared times sail area times lift coefficient.