This is impossible to nail down, but I tried to lay out some guidelines earlier. Since this is one of the most common questions when it comes to camp stove use, I'll get into detail here.
Remember the little green propane bottles are 16 ounces - the big white tanks are 20 pounds. That means you'll need 20 little bottles to equal 1 big tank.
20 green bottles = 1 big white tank
16 Ounce Bottle Cook Times
One little green bottle will probably last a family of 4 people about 2 days of regular cooking. It may last longer if you only cook limited meals. Cooking for a single person or a couple, these little 16 ounce bottles can last up to a week of limited meals.
20 Pound Tank Cook Times
One 20 pound tank will cook limited meals for a full-size family for weeks. If you're cooking breakfast, lunch, and dinner on it expect about a week of use. As always gas time will change depending on how often and how high you're running the burner.