How much space is needed?
The RSPCA puts the minimum for a pair at about 0.7 m² — an enclosure of 120×60 cm — and considers 1 m² and above preferable. And that is a minimum, not a target. Length matters more than levels: guinea pigs do not climb, they run, so a long low enclosure always beats a tall cage of the same area.
Source: RSPCA