These sales numbers are based on the platinum certifications awarded by the Record Industry Association of America. A platinum certification is given when a record sells a million copies, so the current certification is rounded down from the actual sales figures. These numbers only include sales in the United States, which is historically the largest market for music in the world. Also, please note that the RIAA counts sales of double CD sets as a sale of two CDs, so all double albums have inflated platinum certifications. To adjust for this, the sales of double albums have been halved for this list. So, for example, Pink Floyd’s The Wall places at 43 instead of 4 on the list, and Outkast’s Speakerboxxx/The Love Below is bumped off the list entirely.