The free energy of N=2 supersymmetric AdS_4 solutions of M-theory

We show that general N=2 supersymmetric AdS_4 solutions of M-theory with non-zero M2-brane charge admit a canonical contact structure. The free energy of the dual superconformal field theory on S^3 and the scaling dimensions of operators dual to supersymmetric wrapped M5-branes are expressed via AdS/CFT in terms of contact volumes. In particular, this leads to topological and localization formulae for the coefficient of N^{3/2} in the free energy of such solutions.