The mean coefficient of linear thermal expansion is used to define a new “instantaneous coefficient of linear thermal expansion” (ILTE) which is proved to be independent of reference temperatures required to define mean values. Hence it can be considered a true material property. The new ILTE provides a common reference to compare thermal expansion data of different materials. This instantaneous coefficient is different from the instantaneous value defined by ASTM standards. Values of the new coefficient are compared with the widely used mean coefficient values. Accuracy of calculations using the new ILTE is demonstrated using the mean coefficient data of two materials.