How many pigs can this cage hold?

I would say six or seven girls, or five boys, given that 3 pigs' recommended floor grid space is 10 (i.e. a 2x5) and boys need a little more room.

Only the bottom/main floor counts toward space.

About 7 maybe 8 sows if they get along well and up to no more than 7 boars. This is based on the minimum size main level for each sex and then you add at least a 1x2 section for each additional pig you want to add. The upper level doesn't count towards the square footage.

If you are getting piggers for the first time though, I recommend you start with a pair and see how you do with those before getting a whole herd.