This document describes a method for determining the section loss (Fig. 1) of deformed and square, uncoated, round, reinforcing steel bars due to damage, corrosion, or both. A similar procedure can be used to determine the section loss of deformed square and twisted square reinforcing steel bars due to damage, corrosion, or both. Reinforcing bar section loss is the loss of cross-sectional area that can reduce the load-carrying capacity of a member. Section loss is typically caused by corrosion of the reinforcing bar or construction damage, such as saw cutting or drilling into a reinforcing bar.