How long do fuel canisters last?

There are many variables.

One stove I own is specified to boil two liters of water on 1 ounce of butane blend fuel. However, they don't state the starting temperature or the conditions.

–B.G.–

It depends

8 ounce net canister = 32 pints?

You should weigh it before and after, remember how many cups you boiled, and figure it out for your situation

There are many threads and articles about this

Article by Will Reitveld here:

http://www.backpackinglight.com/cgi-bin/backpackinglight/lightweight_canister_stoves_test_report.html

Covers your question, based on testing a number of different stoves under various conditions. Subscription to read full text, I believe.

Example: He estimates "gas mileage" for a Snow Peak Gigapower (my stove) under field conditions at around 8 quarts (~ liters) per 4 oz canister. "Field conditions" mean moderate flame, variable wind, and some sort of wind screen.

Wind screens for canister stove is another topic (and one you should research), but performance will be pretty bad without.

Edit: Obviously, 4 oz canister ~ 8 qts. is consistent with Jerry's answer above, and the spec on Bob's stove.

here is another article I have found useful and have referenced a few times.

http://www.backpackinglight.com/cgi-bin/backpackinglight/comparative_fuel_efficiency_and_weight_of_stoves_pt2.html