In this work, a novel approach to modeling the total leakage current of an entire circuit is presented. Algebraic Decision Diagrams (ADDS) efficiently capture both the leakage values and the underlying Boolean functions of the circuit, and can return a circuit's total leakage current for any possible combination of primary inputs. These ADD leakage models are created without performing any circuit-level simulations, and their hierarchical approach gives them the ability to capture leakage values from any available leakage model. Various rounding and variable reordering algorithms are used to reduce the model's size and creation time to a small fraction of the original at the expense of accuracy. Because ADDs do not scale well to large circuits, a second method which breaks the model down into a series of smaller ADDs is also proposed.