  We compute the finite-size corrections to the free energy, internal energy
and specific heat of the critical two-dimensional spin-1/2 Ising model on a
triangular and hexagonal lattices wrapped on a torus. We find the general form
of the finite-size corrections to these quantities, as well as explicit
formulas for the first coefficients of each expansion. We analyze the
implications of these findings on the renormalization-group description of the
model.
