71 Organic systems have been analyzed to understand the relationship of volumetric molecular thermal expansion (TE M ) or volumetric thermal expansion coefficient (α v ) with the molecular volume (V M ), molecular surface area (S M ), % of heteroatoms, and hydrogen bonding. TE M is found to increase linearly with increasing V M and S M . However, it has been observed that the TE M per unit S M is ∼182 Å•MK −1 , which does not depend upon V M but decreases with an increasing % of the number of heteroatoms in the molecule. This also indicates that the average molecular radius increases by ∼182 × 10 −6 Å when the temperature increases by 1 K. Therefore, α v of the systems increases with the increase in molecular surface area per unit volume, and hence, smaller molecules possess a larger α v than the larger molecules. This also happens because the number of covalent bonds is larger, and the number of weak supramolecular contacts is smaller per unit volume of the crystal for larger molecules than for smaller molecules. Few hydrogen-bonded systems, which possess a high number of hydrogen bonds per molecule (N HB ) per unit volume, are found to exhibit smaller α v , and α v •N HB /V M increases linearly with 1/V M .