Great large size that I couldn't find in the pet stores.  I recently moved my 8 year old cat's box to the basement.  He's a big boy, ragdoll weighing in at 18 lbs, and insisted on using a tiny litter box he had as a kitten.  The little box was in the bathroom, and I use flushable litter.  His tiny box issues included lots of misses, and poop in the hall when his tiny box wasn't clean.  Fast forward and thanks to Amazon, I ordered two of these large litter boxes and mats for the basement box move.  Believe it or not, I couldn't find this size in any local pet store - I have no idea why they wouldn't carry them, but they didn't.  My big boy is happier with two big boxes (one for poo and one for pee) and the mats keep the litter mess contained.  I don't remember what I paid for them, but whatever it cost, it was worth it.