Naw its not really huge... if you think it is then great thats the whole point ...im trying to give my animals space... not everyone wants to keep their snakes in a 12qt tub. As far as the measurements the top is wider than the bottom... all rubbermaid tubs kinda go in at an angle from top to bottom and theyre not straight down. Im assuming thats where the measurment differences comes into play. Either way my sinakes have plenty of room and they use the whole tub so I will always house mine in large tubs. I believe that you should offer all pets the most room possible as long as youre still meeting their needs. Thas just how I do.