Bed frames are designed to fit standard bedding.
In the USA, standard bedding sizes are:
Twin: 39″ X 75″
Twin XL: 39″ X 80″
Full: 53″ X 75″
Full XL: 53″ X 80″
Queen: 60″ X 80″
King: 76″ X 80″
California King: 72″ X 84″
The actual size of your bedding may vary depending on the manufacturer of your mattress set. It is important that you MEASURE YOUR BOX SPRING to make sure you order the correct size bed frame. Many bed frames are designed to fit one size only. (Some bed frames fit twin, full, queen, and king, but not all.)
MEASURING YOUR BOX SPRING IS especially critical when you are ordering KING or CALIFORNIA KING size. There IS a difference, and the two sizes are often confused, even by people who sell furniture and bedding. If a salesperson tells you that he is selling you a KING size bed frame or mattress set, DO NOT take his word for it. We cannot stress enough how important it is to MEASURE YOUR BOX SPRING! If you have a KING size box spring, it will be approximately 76″ wide by 80″ long. If you have a CALIFORNIA KING, your box spring will be approximately 72″ wide by 84″ long.
I recommend measuring your box spring, rather than the mattress, because the box spring will actually be the part that fits into the bed frame.