Formula unit (or molecular) volume, "V[subscript m]", is related to many thermodynamic and physical properties of materials, so that knowledge of "V[subscript m]" is useful in prediction of such properties for known and even hypothetical materials. The symbol "Z" represents the number of formula units in a crystallographic unit cell; "Z" thus permits calculation of "V[subscript m]" from the unit-cell volume. Unfortunately, "Z" is sometimes omitted from published crystal constants (for obscure reasons). We discuss methods for evaluation of "Z" and "V[subscript m]", and some of the complications in the assessment of "Z". We show how entropy, lattice energy, and bulk isothermal compressibility (a thermoelastic property) are calculated using thermodynamic correlations, with the chalcopyrite CuAlS[subscript 2] as an example. (Contains 5 figures and 1 note.)