Thanks for the reply. The reason this maters is I plan to make a matched set. HLT, MLT,BK, and conical fermenter. I'm thinking I want about 25 gallons post boil miniumum, but also considering using 55 gallon plastic barrel fermenters with which I would want about 40 gallons post boil. So this problem factors in to the size of every other piece of equipment and what size sheets of metal I will be ordering. As far as I can tell so far, air temp, humidity, and surface area are the biggest factors. From what I've read Beersmith doesn't account for these factors accuratlly. It makes a big difference at $200 - $300 a sheet for 18 gauge 304 stainless.