Abstract: A Piano Key (PK) weir is a type of nonlinear (labyrinth-type) weir developed specifically for free-surface flow control structures with relatively small spillway footprints. There are many geometrical parameters which influence the discharge capacity of the PK weir. The discharge capacity is a functional characteristic of geometrical parameters. To have a better understanding of the effects of PK weir geometry on discharge capacity, three PK weirs of varying geometrical parameters were physically tested in the laboratory. For each design the discharge was measured by keeping constant upstream depth and noting down the downstream depths at various sections for respective upstream depths. From the experimental results, Cd and Qa values were found to be different for all configurations. The values Cd and Qa were found to be dependent on various parameters viz., inlet width (Wi), outlet width (Wo), floor slope and parapet wall. The Weir height (P) and the width of the Weir (w) were kept constant for all the three Weirs. Also the profile of nappe in the downstream length was plotted for each model for different upstream depths and comparisons were made.