We can have three cats in a studio apartment and they will be fine. Or we could have one cat who needs a whole house!
It all depends on their energy level.
Cats need far less space than a dog. It's not about size. It's about the different ways cats and dogs manage their energy.
Dogs are marathoners, bred for long hours of service. Without enough exercise, dogs become anxious, aggressive, and destructive.
Cats are sprinters. They store up energy while waiting patiently for their prey to give them an opening, and then explosively release it all at once.
We don't need a big space, but we do need the right kind. Kittens need a lot of exercise, but the fully mature cat, going all out, is actually the most demanding. Big-boned, sturdily built cats love the "ground game" and will need runways to race over. If we have lean, long-bodied cats, they are more likely to be over the couch, through the magazine rack, and up the drapes in less time than it takes for us to read this sentence.
We can increase our cat space by adding more vertical surfaces, or opening up carpeted areas for them. But there is another factor in our requirements, and that is how well our cats get along.
Those three cats in the studio apartment can get along fine if they are older cats who are friends. But any two cats who don't get along will find a whole house... isn't big enough.
To figure out how many cats in a given space, and more information on how the different types get along, see my Cat Space Calculator.