Very few rigorous laws are known to define the ‘disordered’ structure of metallic glass (MG) and correlate its structure with properties. Recently we found that under simple compression, the volume (V) of a MG changes precisely with the 2.5 power of its principle diffraction peak position (1/q1). Here, we determined the V and q1 of a Ce68Al10Cu20Co2 MG under pressure, and found that the 2.5 power law holds even through its polyamorphic transition. The transition is, in effect, equivalent of a continuous compositional change of 4f-localized Ce to 4f-itinerant Ce, indicating the 2.5 power law is general for tuning with composition. We further reexamined the previously reported compositional power law exponent of 2.3 on seven different MGs, the more precise determination also yielded the exponent of 2.5. The exactness and universality of the 2.5 power law suggest a general packing scheme in MGs imposed by the good glass forming ability.