Abstract: A curved or higher-order surface, such as spline patch or a Bézier patch, is rendered pixel-accurate if it displays neither polyhedral artifacts nor parametric distortion. This paper shows how to set the evaluation density for a patch just finely enough so that parametric surfaces render pixel-accurate in the standard graphics pipeline. The approach uses tight estimates, not of the size under screen-projection, but of the variance under screen projection between the exact surface and its triangulation. An implementation, using the GPU tessellation engine, runs at interactive rates comparable to standard rendering.