The more space you can give guinea pigs the better. They need lots of space to exercise and play to help them maintain a healthy weight.
The most accepted recommendations for cage size are:
2 guinea pigs – 7.5 square foot minimum – 10.5 square foot is better
3 guinea pigs – 10.5 square foot minimum – 13 square foot is better
4 guinea pigs – 13 square foot minimum – more is better
This means that many pet store enclosures are far too small.
When considering cage size, only one level of space is counted. This is for several reasons. The main reason is that not all guinea pigs will use a ramp to go up to a second storey. So, if you do have a two storey home for your piggies, the second storey is technically bonus space on top of the recommendations above.
Another thing to consider is whether you have males or females. Generally pairs or groups of males will need more cage space than recommended above to reduce the risk of fighting.