The average size of a U.S. jail cell is 6 by 8 feet, or roughly 48 square feet. The size of the cell varies based on institution, occupancy and level of security.
The size of a jail or prison cell depends upon the age of the institution, many of which have been in existence for decades. Different states and institutions have different standards regarding cell size. For example, as of September 2014, the Florida Department of Corrections website states that cells within the Cell Housing Unit range in size from 7 by 8 feet to roughly 11 by 14 feet. The Texas Commission on Jail Standards states that cell size should be determined by the number of inmates confined at a time.
Additionally, Supermax prisons for violent criminals posing a high security risk often have larger cells to allow for segregated long-term housing.