I carry a 5 pound tank. A tank that size should easily last you 10 days if you're just using it for cooking. I've probably camped at least 20 days since I last refilled mine and it still has plenty of gas in it.
One pound of propane equals approximately 20,000 BTUs. I have a 10,000 BTU stove. I rarely turn my stove on full blast unless I'm trying to boil water very quickly. I guess in general I'm using around 5,000 BTUs or less at anytime.
I believe tanks are generally filled to about 80% capacity. So a 5 pound tank would actually be "full" with 4 pounds of propane. This would be approximately 80,000 BTUs. So running at 5,000 BTUs implies around 16 hours of use. That should be more than enough for 10 days of cooking.
Recommend you pick up a gauge as well for the tank. It's helpful to know when it's almost time to refill.
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