So many variables to consider : -
a) Bowl size and shape. I have pipes ranging from Group 1-6. My preference is a Group 3-4 which usually gives me a 30-40min smoke.
A wide shallow bowl will smoke faster than a tall, narrow one generally.
b) Cut of tobacco. Finer cuts will burn faster. A rubbed out flake will smoke a lot faster than a folded&stuffed one
c) The moisture content of the tobacco - the drier the better and faster it burns.
d) Prevailing weather conditions. Is it windy or a really humid day ?
e) What you are doing while smoking. I never smoke while I am doing something active as that makes me puff faster. Reading is my favourite activity while I have a smoke as I find it relaxing.
If I'm smoking in company, it'll take a lot longer, as we chat and shoot the breeze.
f) Your puffing cadence. Some like it best when the tobacco is just about to go out. Me, I like to keep it smoky. If the bowl feel hot, I know to slow down.
g) How much time do you have ? If I've set aside 90 minutes for a smoke and I finish in an hour, or if I haven't finished reading the papers, I'll just fill another pipe, light up and sit back and enjoy