size (n.) Look up size at Dictionary.com
c.1300, "an ordinance to fix the amount of a payment or tax," from Old French sise, shortened form of assise "session, assessment, regulation, manner" (see assize), probably a misdivision of l'assise as la sise. The sense of "extent, amount, volume, magnitude" (c.1300) is from the notion of regulating something by fixing the amount of it (weights, food portions, etc.). Specific sense of "set of dimensions of a manufactured article for sale" is attested from 1590s.
size (v.) Look up size at Dictionary.com
c.1400, "to regulate," from size (n.). Meaning "to make of a certain size" is from c.1600; that of "to classify according to size" is first attested 1630s. Verbal phrase size up "estimate, assess" is from 1847 and retains the root sense of size (n.). Related: Sized; sizing.