We draw attention to the relationship between volumetric change and glass-forming ability (GFA) in various metallic glass-forming alloys. The critical cooling rate can be expressed as Rc=2.5×10−5exp(5.0×102Vlg), where Vlg is defined as (Vl-Vg)∕Vl. We specifically plot the temperature dependence of specific volume for Ca65Mg15Zn20 alloy, and then demonstrate that the larger slope between Vl and Vg, closely related to thermal expansion coefficient, corresponds well to the GFA of the alloy. This insight can provide a clue if the correlations are to be used in the appreciation of glass formation and in the development of an alloy system with enhanced GFA.