A magazine's circulation is the number of copies it distributes of an average issue, be that weekly, monthly or at some other frequency of publication. It is one of the principal factors used to set advertising rates. Circulation is not always the same as copies sold, often called paid circulation, since many magazines, especially those dealing with business and professional topics, are distributed without cost to the reader. Readership figures are usually higher than circulation figures because of the assumption that a typical copy of the magazine is read by more than one person. In many countries, circulations are audited by independent bodies such as the Audit Bureau of Circulations to assure advertisers that a given magazine does indeed reach the number of people claimed by the publisher.
