For a 55 gallon aquarium I have a set of slate pieces that when easily aranged cover the back wall with a nice natural slate backdrop. These aren't precision cut rectangles - but a set I pieced together that do a great job and probably better. I've had and used htem for more than 30 years here. I no longer have the aquarium and these either need to go or be turned into garden path stones. But they work so well I'd love to have somebody take them for their aquarium. So basically full width and basically full height. Note you can still use back mounted aquarium equipment. Maybe half inch thick at most? I have really enjoyed these over the decade. Let me know and I'll set them by the mailbox and provide address. All the best! Mike