What is...Extent?
Extent is the physical quantity of archival records. Different archives measure extent in different ways, but they still are measurements for understanding how much material there is and how much room it takes up.
Extent may be measured in a variety of ways. The traditional method was to measure collections in linear feet. However, square feet are often a more popular method today as they can be used with modern technology to more efficiently utilize shelving space.
Some collections may also be measured by the physical format of the media such as volumes or microfilm reels.
Collections can vary greatly in size, and the size of a collection can help the researcher learn more about what is available. For example, some Special Collections are extremely small; they may only have a single item such as a letter or telegram in the whole collection. Other collections may be significantly larger, and constitute hundreds of boxes.
Where available, reviewing the extents of series or other parts of a record in the finding aid may offer a better understanding of what types of records were retained are most likely to be extant. For example, the Early Sheet Music Collection consists of 13 linear feet of sheet music. 4.5 linear feet are part of the New Orleans Early (1861-1899) series, and only .5 linear feet are from the New Orleans (1899-1953) series. Researchers looking for New Orleans music from the 19th century are more likely to locate what they are looking for than researchers looking for New Orleans music from the 20th century.
Extent differs from extant, an archaic term for records that currently exist. When two volumes of a record are extant they are all that are in our collection. If additional volumes are held elsewhere or ever existed is unknown.
Learn more:
National Archives and Records Administration: The National Archives Catalog
Society of American Archivists: Dictionary of Archives Terminology