While national magazines are not required to publish their circulation numbers, most do anyway — especially the larger periodicals dependent upon advertising revenue. This is because advertisers typically favor periodicals that have certificates of circulation, such as those granted by the Audit Bureau of Circulation.
The following reference directories collect and publish magazine and newspaper circulation numbers:
- Audit Bureau of Circulation
- Gale Directory of Publications and Broadcast Media
- Ulrich's Periodicals Directory
- The Serials Directory
- Standard Periodical Directory
Of these, the "Gale Directory of Publications and Broadcast Media has the largest reference archive of circulation numbers, which extends back to 1880. At that time, it was called "N.W. Ayer & Son's American Newspaper Annual."