Abstract: Performance based design necessitates the accurate calculation of deformation capacity of structures to satisfy the explicit deformation demands. The procedures to evaluate the sectional curvature ductility and drift capacity of fiber reinforced polymer (FRP) retrofitted circular concrete columns under simulated seismic loading were studied in this paper. The sectional yield curvature was proposed based on numerical analysis results. The computing formula of an ultimate curvature was established from test results. It was found from test results that the plastic hinge length of FRP-confined circular concrete columns is closely related to the amount of FRP. Data regressions were employed to formulate the plastic hinge length from test results of 29 large-scale columns. The reason why larger amount of FRP beyond a certain value can decrease the plastic hinge length was discussed. The relationship between the amount of FRP and axial load ratio to drift capacity of FRP-confined circular concrete columns was investigated from a parameter analysis. Then the upper bound of the amount of confining FRP for an efficient retrofit was suggested.