These are small but were perfect for my mini dachshund puppy. Its was the first toy he was able to squeak and was light enough he could carry it around and shake it. My older dogs did not like the fact it didnt have stuffing for them to destroy but they got over it eventually.
I just love these little guys. I ordered two of the smallest ones, and I admit that they are very small. However my two 5lb - 6lb pomeranians just love them. I love the lack of stuffing, no mess.
If you have a dog/puppy under 15lbs I would order the smaller one. Any bigger I would go with the 18' inch.
I didn't realize when I purchased these that they would be THAT small, and figured 12 inches was plenty. Yet, it's only maybe two inches across, and quite flimsy. It would probably be fine for a chihuahua or other small dog, but it has the strength of a sock at best. Didn't think it was worth the money.