The floor-space numbers for guinea pigs
For two guinea pigs, 7.5 square feet is the accepted minimum — that is a cage roughly 30 by 36 inches — and 10.5 square feet, around 30 by 50 inches, is the size where you start seeing the behaviour you got guinea pigs for: full-speed laps, popcorning, and two pigs choosing to rest apart without it becoming an argument. Boars need more room than sows as a rule, and a trio needs the next size up again, not the minimum squeezed harder. Measure the inside floor, not the flared top of a plastic base, which overstates the space your pigs actually stand on.
One level, and why tiers do not count
Guinea pigs are ground-dwellers with short legs and long bodies. They are not climbers, and a steep ramp to a shelf is furniture they mostly ignore or fall from, so levels never add to their usable space the way they do for rats or ferrets. What they need is one continuous run of floor: long enough for a proper sprint circuit, wide enough for two pigs to pass without a confrontation at the hay rack. A grid-style pen built from modular cubes is the easiest way to hit these sizes, and it can grow by a panel when the herd does.
Laying out the space so it works
Guinea pigs feel exposed in open ground, so a big empty cage can paradoxically make them hug the edges. Fill the floor with two hidey houses — one per pig, each with two exits so nobody gets cornered — a hay area big enough for a pig to sit in, tunnels, and a fleece forest or draped corner for cover. Put food and water at opposite ends so a shy pig is never priced out of both by a bolder cage-mate patrolling one spot. Solid flooring only, with fleece liners or deep paper bedding over it; wire floors injure feet and invite bumblefoot.
Signs the cage is too small
A cramped herd tells you plainly: squabbles that escalate from chattering to lunging, one pig permanently exiled to a single hidey, bar-chewing, and pigs that sit hunched and inactive instead of grazing and exploring. Weight creep is another slow signal, because pigs in a small cage simply move less. Before blaming personalities, add space — many dominance spats between boars evaporate in a pen a panel wider, with duplicated resources so there is nothing worth guarding.
When the whole family helps with a herd kept in the middle of the home, KinsLe Family Sharing puts the cage layout, the veg rotation and each pig's quirks on one shared profile, so whoever feeds them works from the same setup you planned.