It's 2". But honestly, a lot of people have complained that the tea light runs out of fuel before reaching a boil so you might want to reconsider. It's good for less than 2 cups of water but in some conditions, you'll probably want something with a little more capacity if you're planning on boiling more than 2 cups of water. Wedding tins work well. A friend of mine just uses the same cat food can that you would use for the Supercat as an open burner and he's happy with it.