I figured it out using my use and average cost per pound (and the more liberal 4g a bowl). If I buy 1 lb of tobacco every month, I will have enough cellared by the time I'm 63 years old to last until I'm 85 (about when most of the men in my family die). Not too shabby and I get to catch all the new blends. So if I buy some bulk that I always like and a few tins here and there for fun, I should be pipe smoking for the rest of my natural life. Of course, I will be buying more lbs when money permits, because the price ain't gonna go down any time in the forseeable future.