File size

File size is a measure of how much data a computer file contains or, alternately, how much storage it consumes. Typically, file size is expressed in units of measurement based on the byte. By convention, file size units use either a binary prefix (as in megabyte and gigabyte) or a metric prefix (as in mebibyte and gibibyte).

When a file is written to a file system, it may consume slightly more disk space than the file requires. This is because the file system rounds the size up to include any unused space left over in the last disk sector used by the file. A sector is the smallest amount of space addressable by the file system. The size of a disk sectors is several hundred or several thousands bytes. Although smaller sector sizes allow for denser use of disk space, they decrease the operational efficiency of the file system.

The maximum file size a file system supports depends not only on the capacity of the file system, but also on the number of bits reserved for the storage of file size information. The maximum file size in the FAT32 file system, for example, is 4,294,967,295 bytes, which is one byte less than four gigabytes.

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