The pressure loss coefficient of a flat-plate damper for ducted air systems has been determined using computational fluid dynamics (CFD) and experimental measurement. The constant-injection tracer-gas technique and a pitot tube were used to measure mean air velocity in a square duct fitted with a damper. Pressure distribution along the duct was measured using static pressure tappings. The pressure loss coefficient was calculated from the measured pressure loss and mean velocity for the duct fitting. CFD was used to predict airflow and pressure distribution in the duct. The predicted pressure loss coefficient was generally in good agreement with experimental results. The pressure loss coefficient for the damper was found to be sensitive to the clearance between the fitting and duct as well as the degree of damper opening.