We ordered a small for our 25 lb dachshund/beagle and a medium for our 60lb rott/german shephard. They fit perfectly in them, if I were to buy them again I would maybe go up a size on each so they had a bit more room but they love these beds. I would say the small is perfect for a very small dog or cat. I have washed these several times and they show no wear, also they don't attract fur like other beds we have which is great. Best beds we have bought, will definitely be getting all West Paw beds from now on.