Protective oxide scales are critical in corrosion resistance, but predictive models of their growth from the nano to mesoscale is lacking. The growth rate depends upon the system’s thermodynamics, diffusion kinetics, and electrostatics, which result in transport equations that cannot be solved analytically. Recently the phase field method has emerged as a successful tool for modeling the growth laws of oxides across various length scales, but current models still rely on empirical input to fit experiment. In order to develop a predictive tool for early stage oxidation, we have formulated a novel phase field model of oxidation compatible with input from atomic scale theory. The phase field method couples the reaction thermodynamics, diffusion, and electrostatics within the governing equations, and resolves the defect electrochemical potentials throughout the oxide. Using this method the growth rate of oxide scales is determined as a function of oxygen chemical potential, temperature, and applied potential.