Dear Josh,
Yes, it's possible. However, a lot of calculations must be done. The calculations will be based on assumptions which may or may not be true. So, the easiest way to figure out the gas consumption is to get in contact with a torch manufaturer and ask him which are the average consumptions.
Take into account that:
a) torch sizes (at least in Brazil) are identyfied by a number, regardless of who's the manufacturer. So, any manufacturer will be able to answer that question.
b) the consumptios he'll inform you are AVERAGE ones. Anyway, they'll be more reliable than the ones you may calculate.
Giovanni S. Crisi
Sao Paulo - Brazil