A gal of alcohol only weighs 7 lb. Water weighs 7.5lb. That means 1/2 oz of fuel puts out 340 BTUs., but this ain't rocket science so I hope you'll forgive me. But heck! Do you want to do math or do you want to go hiking?

You'll want to do the math for yourself and for the food you like to eat on the trail. I carry a quart of fuel. That's approx 30 oz. If I allow about 1/2 oz at a time to boil water for coffee that 30 oz could be used for 60 cups of coffee, or 30 cups of coffee and 30 packets of instant oat meal, or eight freeze dried packets, four ramin packs, six oatmeals, a couple of pancakes and eighteen cups of coffee. See? You'll want to do your own math for any precision hiking you might do.

Note we've field tested 1/4oz fuel allotments for making coffee, noodles and mash (oatmeal). A thrifty hiker might be able to subsist on 1/4oz fuel increments maximizing their overall equipment weight efficiency.

Plus I would imagine, mountain climbers, for example, know their gear inside and out. So if you're going to do anything that you need to depend on, test it out first and make sure you know how your gear will perform. Cook yourself a couple of meals out in the back yard and see how much fuel you'll use.