A reduction‐to‐parts (RTP) method has been developed to approximate the acoustic impedance of a cylindrical shell with hemispherical endcaps. The approximation greatly reduces the computational effort required to calculate the acoustic impedance as compared to discretization methods and a variational formulation. The shell is subdivided into three parts, two hemispheres and a finite‐length cylinder, which can be considered as subregions of separable geometric shapes. Surface displacements from the original shell are applied to these separable geometries, and the corresponding calculated surface pressure responses are mapped back to the original shell. An approximation to the acoustic impedance of the original shell is calculated using the prescribed displacements and the mapped surface pressures. The accuracy of the approximation is improved in the low‐frequency range when pressure generated on neighboring parts is taken into account. To verify the approximation, the surface and far‐field responses due to a point load are compared with the responses calculated using a variational formulation. The RTP method accurately predicts the near‐ and far‐field acoustic pressures.