The recommended maximum occupancies given on this site are intended to provide a guide to the number of rats that a cage is suitable for, calculated purely using the volume of the cage.
In general, the larger the cage the less room needs to be allowed per individual rat (e.g. groups of 10 or more could cope with just 1.5 cubic feet each), and the smaller the cage, the more room needs to be allowed (e.g. a group of only 2 rats still needs as much space as a group of 4). The background of the rats themselves also needs to be considered, as occasionally rats from certain backgrounds might become nervous or territorial if given a very large space, whereas others may become depressed in a small space.
The number of rats that will live happily together can also be influenced by age, activity levels, sex, temperament and cage furnishings. Space within a cage must be available to the rats, via shelves, hammocks, ropes etc. A tall cage with few accessories will not house as many rats as a properly furnished cage.
Remember rats need room to run around, to climb, to stretch out to sleep and to stand up straight on their hind legs, and there needs to be enough room to provide them with a suitable amount of enrichment. If you currently have baby rats you should bear in mind that does are likely to grow to about 7-10 inches (18-25cm) long (plus tail) and bucks to about 10-12 inches (25-30cm) long (plus tail).
Fancy Rats Team