This all depends on the type of room you book. In general, rooms are sold on double occupancy, which means two adults per room. However, some rooms have additional bedding that flips down from the wall or couches that provide sleeping area for up to two additional people per room. Some suites also allow for up to four sleeping guests. If you plan to lodge more than two adults per cabin, you'll want to double check your room style with your booking agent to ensure proper sleeping space. Keep in mind additional adults beyond double occupancy are booked at a discount rate.
For more info, see Carnival Victory Cruise Ship