This really depends on what uses you want to get out of a rug. If you just want to cover the floor, generally you’ll want one big enough to cover the whole room, with just 2 feet left over on each side. In a nursery, you may just be looking for a soft, safe spot for your child to play. Or you may just want something to brighten up a certain area of the room. The size of the rug doesn’t matter in those cases. You’ll just want to pick one that is big enough to fit your needs.