Fault geometric complexities exhibit fractal characteristics over a wide range of spatial scales (<µm to > km) and strongly affect the rupture process at corresponding scales. Numerical rupture simulations provide a framework to quantitatively investigate the relationship between a fault's roughness and its seismic characteristics. Fault discretization, however, introduces an artificial lower limit to roughness. Individual fault patches are planar and subpatch roughness—roughness at spatial scales below fault patch size—is not incorporated. Does negligence of subpatch roughness measurably affect the outcome of earthquake rupture simulations? We approach this question with a numerical parameter space investigation and demonstrate that subpatch roughness significantly modifies the slip‐strain relationship—a fundamental aspect of dislocation theory. Faults with subpatch roughness induce less strain than their planar‐fault equivalents at distances beyond the length of a slipping fault. We further provide regression functions that characterize the stochastic effect subpatch roughness.