FAQ THE MATTRESSES HOW TALL IS THE CASPER MATTRESS? SEE ALL QUESTIONS HOW TALL IS THE CASPER MATTRESS? The Casper mattress is 10 inches thick. This means the Casper mattress is suited to all standard size sheets — but we always recommend using Casper Sheets! 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 are the dimensions of the Casper mattress? Can I use an adjustable bed frame? What’s the difference between a bunkie board and a box spring?