A universal calibration curve for the accurate determination of particle aerodynamic diameter by the TSI APS (TSI, Inc., St. Paul, MN, USA) operating at various temperature, pressure, particle, and gas properties is proposed. The previous dimensionless APS response function proposed by Chen et al. (1985) uses the Stokes number as the governing parameter and is valid in the Stokesian regime only. In the non-Stokesian regime, an additional non-Stokesian correction factor is needed to correct for the indicated aerodynamic diameters of the APS. The universal curve in the present study is based on the relationship between V*p and Stm, p where V*p = V p/Vg and Vpis particle velocity, Vg is gas velocity at the nozzle exit, and Stm is modified Stokes number. Stm incorporates the non-Stokesian effect and is defined as 24St/(Re*C D), where Re is the flow Reynolds number and CD is the particle drag coefficient. We find that the new calibration curve can predict the particle aerodynamic diameter accurately within 6% of error under different operating conditions and particle/gas properties from the referenced condition without the need to introduce additional correction factors.