Pocket depth refers to the length of the seam located at the corners of the fitted sheet. Generally speaking, the pocket depth will fit 1-3 inches larger than the depth of the mattress. The elastic at the hem of the sheet allows for some stretch; thus oftentimes sites will say “fits up to” several inches larger than the finished pocket size. So when it’s time to make that purchase be sure you know your measurements: mattress height and any toppers you may be using for a comfort layer. The Cool Luxe fitted sheet has a 16 inch pocket depth and will fit a mattress up to 18 inches tall.