What is "file size"

n. (context computing English) The length of a file, often specified in bytes.

File size measures the size of a computer file. Typically it is measured in bytes or bits. The actual amount of disk space consumed by the file depends on the file system. The maximum file size a file system supports depends on the number of bits reserved to store size information and the total size of the file system.

Binary prefixes for powers of 2 (1,024) and decimal prefixs for powers of 10 (1,000) are both in use. The International System of Quantities also allows unambiguous binary prefixes using different names based on an IEC standard, e.g., kibibyte KiB, mebibyte MiB. The traditional KB is usually binary, meaning 1,024 bytes, while the corresponding decimal kB for 1,000 bytes uses a lower case k for kilo.

With typical disk sector sizes of 512, 1,024, 2,048, or 4,096 bytes, decimal prefixes and bits are less suited to describe file systems accurately. For example, the maximal file size on FAT32 is 4  GB−1 B for a binary prefix of bytes, corresponding to 4×1024×1024×1024−1; decimal 4,294,967,295; hexadecimal FFFFFFFF; or binary 11111111111111111111111111111111 in 32 bits.

Traditional units

Decimal for comparison

Name

Symbol

Binary

Kilobyte

KB

2

Megabyte

MB

2

Gigabyte

GB

2

Terabyte

TB

2

Petabyte

PB

2

Exabyte

EB

2

Zettabyte

ZB

2

Yottabyte

YB

2