An open question in studying normal grain growth concerns the asymptotic state to which microstructures converge. In particular, the distribution of grain topologies is unknown. We introduce a thermodynamic-like theory to explain these distributions in two-and three-dimensional systems. In particular, a bending-like energy Ei is associated to each grain topology ti, and the probability of observing that particular topology is proportional to 1 s(t i) e −βE i , where s(ti) is the order of an associated symmetry group and β is a thermodynamic-like constant. We explain the physical origins of this approach, and provide numerical evidence in support.