I have noticed when trying to burn very small amounts of fuel that I end up with the stove out of fuel before I get much done. So I just typically run the 1.5 ounce minimum except if I'm doing something very light duty, like warming a cup of water for instant coffee or something. Also, temperature and air movement outside affects things enough to where there's no hard and fast rule for how much fuel to use for a certain task. But if you fill the stove up towards the bottom of the radius on the inner piece, that's 1.5 to 2 ounces, and you'll get enough BTU's to boil a couple cups of water, a little lower level for smaller jobs. At 1 ounce or less, it just doesn't get going enough to do too much.