A kibibyte (a contraction of kilo binary byte) is a unit of information or computer storage, established by the International Electrotechnical Commission in 2000. Its symbol is KiB.^[1]

1 kibibyte = 2¹⁰ bytes = 1 024 bytes

The kibibyte is closely related to the kilobyte, which can be used either as a synonym for kibibyte or to refer to 10³ bytes = 1,000 bytes (see binary prefix).

Usage of these terms is intended to avoid the confusion, common in describing storage media, as to the ambiguous meaning of "kilobyte". Thus the term kibibyte has evolved to refer exclusively to 1,024 bytes.

The confusion if kilobyte is used to refer to both 1,000 and 1,024 bytes became more substantial when hard drives grew to gigabyte and larger units. If one expects power-of-two values to refer to capacity, and manufacturers use power-of-ten values, the difference could be substantial. With a kilobyte (1024 versus 1000), the difference is 2.4%. With megabyte (1024² or 1,048,576, versus 1,000,000 - a difference of 4.9%. With "gigabytes", if one uses 1024³, the size of a drive would be expected to be 1,073,741,824 bytes per gigabyte versus a mere 1,000,000,000 - a difference of 7.4%.

Confusion can be compounded by the use of both 1,024 and 1,000 in a single definition. The quoted capacity of 3½ inch HD floppy disks is 1.44 MB, where MB stands for 1000 times 1024 bytes. The total capacity is thus 1474560 bytes, or approximately 1.41 MiB.

Adoption of this term has been limited. ^{[citation needed]}

• Kilobyte
• Kibibit
• Mebibyte
• Binary prefix
• SI prefix
• IEEE 1541
• Orders of magnitude (data)