I have this model in an X-Large Andy the other Serta model in a large. I needed a large in this model.  The product description does not state what size this is only measurements so I contacted customer service to find out if it was a large.  They seemed to think so and I ordered it.  It’s much smaller than a large and it was vacuum packed so I would never be able to get it back in the box nor pay the return shipping.  Guess I shouldn’t have taken the chance without knowing the size.  Serta labels them all s-m-l-xl.  Don’t understand why Wayfair doesn’t share that info.