Magnetic gears offer a promising alternative to mechanical gears with the added benefit of contactless power transfer. However, quick and accurate analysis tools are required to optimize magnetic gear designs and commercialize the technology. Therefore, this paper proposes an extremely fast and accurate 2-D magnetic equivalent circuit (MEC) model of radial flux magnetic gears with surface mounted magnets. This MEC model's distinguishing characteristics include a heavily parameterized gear geometry and a parametrically adjustable systematic flux tube distribution which allow for accurate and efficient analysis of a wide array of designs. Furthermore, themodel is fully linearwhich results in very quick simulation run times without sacrificing significant torque prediction accuracy for most practical designs. This is Part I of a two-part paper and focuses on the implementation of the MEC model. Part II validates the accuracy of the MEC model by comparing its torque and flux density predictions with those produced by nonlinear finite-element analysis.