We consider the dimer model on the rectangular 2M × 2N lattice with free boundary conditions. We derive exact expressions for the coefficients in the asymptotic expansion of the free energy in terms of the elliptic theta functions (θ 2 , θ 3 , θ 4 ) and the elliptic integral of second kind (E), up to 22nd order. Surprisingly we find that ratio of the coefficients f p in the free energy expansion for strip ( f strip p ) and square ( f sq p ) geometries r p = f strip p /f sq p in the limit of large p tends to 1/2. Furthermore, we predict that the ratio of the coefficients f p in the free energy expansion for rectangular ( f p (ρ)) for aspect ratio ρ > 1 to the coefficients of the free energy for square geometries, multiplied by ρ −p−1 , that is r p = ρ −p−1 f p (ρ)/f sq p , is also equal to 1/2 in the limit of p → ∞. With these results, one can find the asymptotic behavior of the f p (ρ) from that of the f strip p , whose asymptotic behavior is derived explicitly here. We find that the corner contribution to the free energy for the dimer model on rectangular 2M × 2N lattices with free boundary conditions is equal to zero and explain that result in the framework of conformal field theory, with two consistent values of the central charge, namely, c = −2 for the construction of a conformal field theory using a mapping of spanning trees and c = 1 for the height function description. We also derive a simple exact expression for the free energy of open strips of arbitrary width.