'standard-sized' originates from the combination of 'standard' and 'size', where 'standard' meant 'a level of quality or attainment' and 'size' referred to 'the dimensions or magnitude of something'.

'standard' and 'size' were combined in modern English to form 'standard-sized', indicating conformity to a recognized standard.

Initially, it meant 'conforming to a recognized standard in size', and this meaning has largely remained the same in modern usage.