Which metric prefixes make a standard metric unit larger?

A prefix can not express a unit of length. A unit of length like a mile, foot, inch, Meter is fixed. The largest unit of length I know of is the 'Parsec', equal to just under 31 trillion (31×1012) kilometres (about 19 trillion miles), 206265 AU, or about 3.26 light-years.

A prefix would be applied to one of these units eg 'kilo' (meaning a thousand) e.g. kilometer or 'mega' (meaning one million) e.g. megaparseck.