Why isn't the size of something considered a physical property?

Size is not considered because it does not describe the nature of a given object, but the magnitude of its span.

Explanation:

Physical properties are properties of an object that does not change its composition. They are used to to describe some observable characteristics of the object. Mostly, physical properties of an object can be observed with one or more sense organs.

Size is not usually used when considering physical properties of objects because it describes the magnitude of its span. It does not describe the nature of the object.

Size is not considered a physical property because it is not measurable with concrete data, but a compound of height, weight and volume, which are physical properties by their own.

A physical property is, according to an initial understanding, an individual property, that is, which is linked in particular to any substance.

A physical property has the characteristic of being able to be measured or observed without affecting the composition or integrity of the respective substance. Some examples of physical properties are mass and volume.