The kibibyte is a multiple of the unit byte for digital information. The binary prefix kibi means 210, or 1024; therefore, 1 kibibyte is 1024 bytes. The unit symbol for the kibibyte is KiB.
The unit was established by the International Electrotechnical Commission in 1998, has been accepted for use by all major standards organizations, and is part of the International System of Quantities. The kibibyte was designed to replace the kilobyte in those computer science contexts in which the term kilobyte is used to mean 1024 bytes. The interpretation of kilobyte to denote 1024 bytes, conflicting with the SI definition of the prefix kilo, used to be common.


The unit prefix kibi specifies multiplication by 210. It was derived as a portmanteau from the words kilo and binary, indicating its origin in the closeness in value to the SI prefix kilo. While the SI prefix is written with lowercase, all IEC binary prefixes start with an uppercase letter.
Therefore, the definition of the kibibyte is:
The next larger unit of information in the sequence with IEC binary prefixes is the mebibyte :
IEC specification 80000-13 defines one byte as 8 bits. Therefore,


The kibibyte is closely related to the kilobyte, which equals 1000 bytes, as the prefix kilo is defined in the International System of Units. The kibibyte was established by the International Electrotechnical Commission in 1998,
Prior to the definition of the binary prefixes, the kilobyte generally represented 1024 bytes in most fields of computer science, but was sometimes used to mean exactly one thousand bytes. When describing random access memory, it typically meant 1024 bytes, but when describing disk drive storage, it meant. The errors associated with this ambiguity are relatively small.
In 1995, the International Union of Pure and Applied Chemistry's Interdivisional Committee on Nomenclature and Symbols attempted to resolve this ambiguity by proposing a set of binary prefixes for the powers of 1024. After adopting the proposal, the IEC published the standard in January 1999.
In 1999, Donald Knuth suggested to call the kibibyte a "large kilobyte".
In spite of the formal adoption of the kibibyte, kilobyte continued to be used often to mean 1024 bytes as late as 2007 in some product advertising and other contexts.