Calculation of the mutual impedance between two plane pistons in an infinite plane baffle involves a fourfold integration over the areas of the two pistons. In general, all of these integrations must be done numerically. However, for simple piston shapes, a change of variable can reduce two of the integrations to triviality leaving only two to be computed numerically. Results are presented for half‐wavelength‐diameter circular pistons and half‐wavelength‐dimension square pistons.