Housing rabbits isn't one size fits all. Your home and lifestyle, combined with your rabbit's personality and size, will determine his appropriate living arrangement. In time, you'll figure out what works best for your family. When you first bring your rabbit home, it may not be the best idea to give him free rein of the house. That can come later.
What size cage?
Rabbits don't do well cooped up in a cage all day, but it isn't practical to supervise their antics 24/7. Rather than purchasing a "starter cage," invest in something big enough for your rabbit once they are full grown. Dog exercise pens are a terrific solution.
According to the House Rabbit Society, "one guideline to go by is at least 8 square feet of enclosure space combined with at least at least 24 square feet of exercise space, for 1-2 rabbits, in which the rabbit(s) can run and play at least 5 hours per day." In sum, the cage should be at least five times his size when stretched out; bigger is better!
Mary Cvetan, founder of the Pittsburgh House Rabbit Club, demonstrates enclosure size in her seminars by climbing in to an exercise pen and lying down on the floor. She says there should be enough room for you and your rabbit to both lay down fully stretched out in the enclosure without any head to foot squishing.
Room to roam
Even with the biggest, best enclosure packed with toys, chews, hides, and plenty of enrichment, rabbits will inevitably become bored if cooped up all the time. Rabbits that don't get out of a cage can even develop muscle atrophy. Rabbits are crepuscular, which means he will sleep at night and some during the day, but is ready to play at dusk and dawn. Providing at least a few hours of time for your rabbit to roam or play out of the exercise pen is important for his happiness and well-being. It's no secret that young rabbits and bored rabbits can be naughty buns, It's okay to confine your rabbit to a safe space while you're away from home (chances are he will be snoozing anyway), but be prepared he will be ready to play and socialize when you get home.
Do rabbits need cages at all?
If you're game to let your rabbit join the family free-range style, by all means do so! However, you'll first want to make sure your home is safe and bunny-proofed, and may want to ease in to this arrangement gradually. It is best to go with a pen during times your rabbit can't be supervised at least at first. This will keep him out of trouble, and also help with litter training. Rabbits also enjoy having their own home base. This is a good place to go to sleep at night, where your rabbit will feel safe and secure. Even free-roam rabbits like to have their own "room".