The transversal profile of the rail has a significant influence in railway transportation. Both freight and passenger systems regularly maintain these profiles to a precise shape designed to promote favourable in-service contact conditions between wheel and rail. A rail profile index is often employed as key metric of success of this operation, consisting of a weighted difference between the target profile and the actual profile, measured postmaintenance. Despite their major contribution to maintenance planning and quality control, there is significant uncertainty surrounding the application of these indices, particularly with respect to their correlation to the quality of the contact conditions that they are supposed to reflect. A new framework is described for quantifying wheel-rail contact quality and assessing profile performance, which is then used to map the relationships between index scores and statistical indicators of contact quality obtained through simulations, and between index scores and real-world measured rail wear rates.