I want to say that the wedge should be measured lengthwise as across and then width as to the length down. etc. Someone seemed to think it was suppose to at least be the height of an average person, but it is meant to go beneath your head across the bed not down one side of your body. Actually the length appears it would fit my full size bed with a little extra on eas side, or a queen with some short. I have heart failure and am 38 and have had it since 31 when I got this wedge a few years later from my other grandmother it was a blessing! I use a foam latex pillow with it and it gives me the best possible sleep and comfort. I have a heart pump now and am doing so well I can sleep flat but if I have a cold it still helps with that, as well as being great for my neck and back and helping me breathe better because I also have a sleep apnea. Wedges help in a number of ways, but you have to know what you need for your bed and comfort,. All wedges tend to migrate on the bed, and head wedges have a tendency to walk down the bed as you get up and down off of it, or even during sleep as mine does all the time. Use your imagination to how you want to solve this problem: make velcro straps and attach to frame, or elastic straps you can tuck under top mattress corners to keep it from slipping down, it is a simple fix but may take a little imagination and work.