Mainsail Luff Measurement;

Maxluff is top of boom to 8" Below Halyard Sheave. Use your binoculars to look up the mast if you have questions.

Use a tape measure as below, attach a light downhaul line in case the tape breaks. Metric or English measurements are fine.

Sail measurements are always sail edge to sail edge. Never try to measure pin to pin or center of ring to center 0f ring.

If you measure an old sail, the specs is "sail edge to sail edge pulled to normal sailing tensions" Sails are best ordered by measuring the vessel as indicated.