'family-sized' is formed by combining the noun 'family' + the noun 'size' with the adjectival suffix '-ed' (meaning 'having the size of').

'family' originates from Latin 'familia' via Old French and Middle English; 'size' comes from Old French 'sise' / 'size' (meaning a measurement) via Middle English; the modern compound 'family-sized' is a recent formation in English created by combining these elements to describe product or portion size.

Individually, 'family' originally meant 'household' and 'size' meant 'measurement'; combined and with '-ed' they evolved into the descriptive adjective meaning 'of a size suitable for a family'.