If the boat is in your driveway, set the mast up and measure it. I looked at the specs for my boat at sailrite, all screwy! has me at 33' long, I am 29.5. Mast ht at 37.2 when it is 38.2, calling a 150 genoa 315# when my 155 is 345#.
Measuring is best, unless you can find a very known correct measurement.
She drives me boat,
I drives me dinghy!