Wiktionary
family size
n. (context marketing singulare tantum English) A size for a container of goods, among the largest sizes meant for sale to a householder consumer.
Usage examples of "family size".
The groups were matched in terms of social class, parental marital status, and family size.
The couch in Joe's living room was actually a sleeper that folded out into a family size bed.
On the outside was stencilled Kellogg's Cornflakes, 12 x Family Size and on the inside it was half filled with the same sort of jumble which was lying around the room.