Inhomogeneous intercalation in porous anodes may lead to accelerated lithium plating during fast charging. This reaction inhomogeneity can occur both at the particle level or at the length scale set by the electrode thickness. Many studies have investigated the effects of various physical and electrochemical properties (e.g., ionic and mass transport, interface reaction kinetics, electrode thermodynamic behavior) on reaction inhomogeneity. However, their effect on accelerated lithium plating at high C-rates has not been fully elucidated. In this work, theory and experiment are used to study how reaction inhomogeneity and plating are related at high C-rates. It is shown that a non-dimensional number, the “reaction inhomogeneity parameter” λ, can be used to predict plating onset in graphite half-cells with a simple analytical solution derived from porous electrode theory, so long as anode particles are sufficiently small. Experiments measuring lithium plating onset in a small-particle graphite at various C-rates and thicknesses can be normalized to a single “master curve” for plating onset when plotted as a function of λ. These comparisons validate the theoretical predictions from both analytical and numerical modeling. Further, experiments with in situ visual inspection of local intercalation in graphite demonstrate that this λ parameter can predict reaction inhomogeneity measured using various metrics. These combined results support the numerical prediction that reaction inhomogeneity on the electrode length scale is responsible for accelerated plating at high charge rates for small-particle graphite. Further, it is shown with theory that this normalization procedure may be applicable for varied porosity, tortuosity, electrolyte materials and different anode materials. Finally, it is demonstrated that use of this “master curve” can be extended to patterned electrodes where channeled architectures are used to improve high C-rate charging.