When we bought our first rabbit (together/since poor childhood ownership) we bought a cage from pets at home. The store we bought him from didn’t have any larger cages – though we hassled and hassled them over it. Our newest buns came from the same chain but from a branch that sold much bigger cages.
We intended to keep our bunny free range, so his cage was a tiny 95cm x 57cm x 46cm. He was free roam 24/7, excluding room checks which happened maybe once every other month at most. It is no longer sold for rabbits, which is good.
Our present buns are also dwarf breeds and they’ve not been shut away for more than 6 hours (overnight). We had/have to leave them for an extended period last night/today/tomorrow, so we moved them to the part of the kitchen we could reliably section so they had considerably more room for the night.
The RSPCA recommends that for two medium sized bunnies, the cage should be a minimum of 152.4cm x 60cm x 75.2cm BUT this cage size also needs to be connected to a larger ‘run’ where the bunnies can exercise.
Based on this I’d say a cage of 400cm x 200cm/4m x 2m would be appropriate.
Many people say buns should be allowed to free roam for at least 4 hours a day with a cage that size, they could probably get away with less but unless they have a bunny friend they’d be very lonely.
My cage is no longer listed as a size for bunnies, I’ve discovered. I’m not posting the size because I don’t want anyone to think it would be appropriate for anything less than near constant free-roaming.