Thermodynamic properties such as entropy, among others, have been shown to correlate well with formula volume, thus permitting prediction of these properties on the basis of chemical formula and density alone, with no structural detail required. We here extend these studies to the thermoelastic property of isothermal compressibility, 13. We show that compressibility is strongly linearly correlated with formula volume per atom pair, V-pr, for binary solids, with the alkali halides having a proportionality constant of 0.908 GPa(-1) Vpr(-1) while 1:1 monoxides, monochalcogenides, monopnictides, and chalcopyrites (ABX(2), which may be considered as AX plus BX) have a common compressibility proportionality constant of 0.317 GPa(-1) V-pr(-1). Oxides with closely packed oxygen lattices (such as Al2O), garnets (such as Y3Fe5O2 = 4M(2)O()), spinels (MgAl2O = MgO - Al2O), and other oxides (e.g., FeTiO3 = FeO-TiO) have compressibilities which are only slightly dependent on volume, at about 0.108 GPa(-1) V-pr(-1) + 0.003 GPa(-1).