what it should be is the following:
Mainsail = (P x E) / 2
100% Jib = ( I x J ) / 2
Mizzan = (PY x EY) /2
"P" is the luff length of the mainsail, measured along the aft face of the mast from the top of the boom to the highest point that the mainsail can be hoisted or black band.
"E" is the foot length of the mainsail, measured along the boom from the aft face of the mast to the outermost point on the boom to which the main can be pulled or to the black band.
"I" is measured along the front of mast from the genoa halyard to the main deck. The main deck is where the deck would be if there were no deckhouse.
"J" is the base of the foretriangle measured along the deck from the headstay pin to the front of the mast.
PY" and "EY" are, respectively the luff length and foot length of the mizzen of a yawl or ketch measured in the same way as for the mainsail.
So for my boat the numbers work out as:
Mainsail area = 40.672 x 14.76 / 2 = 300.15936
Foretriangle 100% = 1 x 22.57 x 47.232 / 2 = 532.9281024
Mizzan = 32.8 x 10.824 / 2 = 177.5136
However, what I have found is a lot sales brochures use 135% or even 155% genoa, which really overstates the sail area.
This site here
lists the formula and measurements for thousands of boats.