Gears are key components of several industrial applications, being subjected to wear during operation. Scuffing, micropitting and pitting are common types of gear failure modes that can happen. The failure analysis is usually performed by visual inspection, and therefore is subjected to human bias. Hence, it is important to implement objective metrics to quantify of these failure modes. In this investigation, the 3D topography of gears exhibiting micropitting, pitting, and scuffing failure modes were measured with a white light interferometer. These topographies were evaluated in terms of function roughness parameters (S_pk, S_k, and S_vk) as per ISO 25178-2. The results of the function parameters highlighted differences in the severity of damage, starting from the micropitting, and increasing to the scuffing and further to the pitting failure modes. Besides, using the peak-to-dale ratio (S_pk⁄S_vk ), it was possible to differentiate the scuffing failure from the micropitting and the pitting failures. This investigation demonstrated that it is possible to perform an objective quantification of gear failure modes using functional roughness parameters.