Coefficient of Restitution Calculator

About this calculator

The coefficient of restitution (e) quantifies how "bouncy" a collision is, defined by Newton's classic ratio e = v_separation / v_approach — the relative speed at which two objects fly apart after impact divided by the relative speed at which they came together. A value of e = 1 describes a perfectly elastic collision that conserves kinetic energy, while e = 0 describes a perfectly inelastic collision where the objects stick together.

Sports equipment designers rely on this exact ratio: it's why golf and tennis governing bodies set legal maximum COR limits on club faces and racquets, why basketballs and bouncy balls are tested for consistent rebound behavior, and why engineers testing vehicle bumpers or packaging materials measure COR to model impact and crash energy loss.

Physics students studying momentum and energy conservation, sports scientists and equipment testers, and mechanical engineers modeling impacts all use this ratio because it captures, in a single number, how much kinetic energy a collision keeps versus loses to deformation, heat, and sound.