Bedlift Kits cannot be installed on beds in slide outs with fixed base non-moveable platform bottoms. Sizes: Bedlift Kit XSmall for short front compartments. 19" - 23" deep Bedlift Kit Small for short front compartments 24" - 30" deep Bedlift Kit Standard for Queen beds with RV style mattresses "NEW SIZE" Bedlift Kit Standard-Lite for Queen beds with lite weight foam mattress Bedlift Kit Large for standard King beds with RV mattresses or queen beds with oversize mattresses and/or heavy pillow toppers installed Bedlift Kit Heavy for King beds with oversize mattreses or thick particle board platform decks