Typically, your sheet size should be compatible with your mattress size. The packaging will identify the standard sizes as twin, full, queen, king, or California king, and will also list the dimensions. If you are unsure about your sheet size, measure your mattress to be sure it will fit properly. Remove all bedding, then measure the width and length of your mattress. Next, measure the height of your bed and remember to include any mattress pads in the total height. These dimensions should match or be slightly larger than the sheets to fit your mattress.