FAQ THE MATTRESSES HOW TALL IS THE CASPER MATTRESS? SEE ALL QUESTIONS HOW TALL IS THE CASPER MATTRESS? The Casper mattress is 12 inches tall. YOU MAY ALSO LIKE Once I take my mattress out of the box, how long does it take to expand? Will my sheets fit on a Casper? What’s the difference between a bunkie board and a box spring? Can I use an adjustable bed frame? What are the dimensions of the Casper mattress?