A standard fitted queen-size sheet measures 60 inches by 80 inches, while a standard flat queen-size sheet measures 90 inches by 102 inches. It may be necessary to measure the mattress before deciding on what size sheets to buy.
There is a lot of variation in standard mattress sizes, especially in depth measurements. Some premium mattresses have an extra 4 to 5 inches in depth, which needs to be accounted in order to ensure fit when purchasing sheets. A pillow-top mattress also adds another few inches to the depth of the mattress. Mattresses with extra depth require special fitted deep-pocket sheets.