Loose tobacco averages out about an hour in a Group 4 (medium sized) pipe. But this is highly variable. Flake can be nursed for much longer, as can plug and rope, and to some degree coin; likewise these can give an hour in one of the smaller pipes. If you take an extra large pipe and pack it with flake, you can get beyond two. I seldom run a bowl right through, but smoke intermittently, spacing the relights, just because I'm poking around at projects, chores, reading, etc. But I'm giving continuous times for this post. Along with medium size pipes, every one can use an extra large and a small pipe or two (or, always, more). On the other hand, dry burleys can finish in twenty minutes in a medium pipe even without puffing or pushing, which if you like the stuff is fine. I do.