The objective of this research was to develop a laboratory test procedure to predict full-scale primary clarifier performance using Chemically Enhanced primary Treatment (CEPT). A method was developed that simulated actual primary clarifier performance, with chemical enhancements, based on simulating full-scale surface overflow rate (SOR) and flocculation time in the laboratory. The method used for this test was adapted from a procedure used for sizing of Lamella Separators. Validation of the developed method was done by comparison of laboratory data, with stress test data from two full-scale clarifiers, at the Blue Plains Advanced Wastewater Treatment Plant in Washington, DC, USA. The results indicated that the laboratory SOR test method could be calibrated to predict and optimize full-scale primary clarifier performance.