To assist you understand sail measurements and their importance in the design and manufacture of a high quality and performance sail we have provided some definitions below.

"J" - the distance from the front of the mast to the spot where the forestay meets the deck.

"I" – the distance from the deck (not the cabin top), to the top of the forestay.

"P" – the distance from the top of the boom to the main halyard sheave, or the black band if your boat has one.  This is best measured by hoisting a tape to the correct height and then reading the distance where the tight tape measure intersects the boom.

"E" – the distance from the rear of the mast to the clew outhaul fitting when fully extended, or the black band. 

Leech  -  is always the trailing edge of the sail

Luff – is the leading edge of the sail

Tack - is where the sail is fixed (tacked) to the deck or boom

Head – is the highest corner of the sail when hoisted

Clew - is the loose corner on a headsail and is at the end of the boom farthest from the mast on a main sail.

Foot - is the lowest edge of any sail