This is a list of magazines by overall circulation. A magazine's circulation is the number of copies it istributes, on average, for each issue. 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 are distributed without cost to the reader. This is especially true for magazines dealing with business and professional topics. Readership figures are usually considered to be 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, circulation figures 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.