This essay develops a formal framework for selecting welfare-enhancing standards of proofs. It reduces the inquiry to one equation with five variables and graphs the decision space in which each standard of proof dominates. The value of that exercise is demonstrated by applying the model in three contexts: (1) private party litigation, (2) government deprivations, and (3) affirmative defenses. In the first two at least, the new framework guides the selection of proof standards better than existing doctrine.