here's my cheat way of finding out....have no clue about a formula but this works SUPER for me. If its a wood log mold, put in a garbage bag, measure water and pour in to 3 inches high. Just take note of how much water you are adding and thats how much base you need. If you are using a plastic mold, obviously do the same, without needing the garbage bag of course! LOL I know write on all my wooden molds the number of oz in pencil so I don't forget how much it holds. Hope this helps ya...or even someone else.