By first motivating the use of the newly developed denominator regularization we show how using it can be used to calculate the $2\to2$ scattering amplitude in a finite sized massive $\phi^4$ theory. We consider a spacetime with periodic boundary conditions and asymmetric sizes of the periodic dimensions. By using denominator regularization we then derive the scattering amplitude which we show is consistent with the optical theorem and infinite volume limit. This showcases one of the strengths of denominator regularization over standard techniques such as dimensional regularization.