Introduction 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. Figure 2 shows examples of reinforcing bars with section loss. This document does not address evaluation of the load-carrying capacity of a member@ or determining if a repair is required. These tasks should be performed by a licensed design professional based on a review of existing conditions (ACI 546R [ACI Committee 564 2014]).