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A mebibyte (a contraction of mega binary byte) is a unit of digital information storage, abbreviated MiB.

1 MiB = 2²⁰ bytes = 1,048,576 bytes = 1,024 kibibytes

The mebibyte is closely related to the megabyte (MB). "Megabyte" is sometimes used as a synonym for mebibyte, or to refer to 10⁶ bytes = 1,000,000 bytes, or even 1,000 times 1,024 bytes, depending on context (see binary prefix for background). For example, the 1.44 MB floppy disk's storage capacity is calculated using 1,024,000 bytes per "MB" (e.g. 1.44 times 1024 times 1000), rather than 1.44 mebibytes (1.44 times 1,048,576). The three numbers are relatively close together, but mistaking the three has nonetheless led to consumer confusion and even legal disputes. There are times when it is necessary to know the exact size of a file, for example, or exactly how much space remains on a storage device, hence the definition of the mebibyte.

The unit was defined by the International Electrotechnical Commission (IEC) in December 1998. Use of mebibyte and related units is endorsed by IEEE and CIPM in contexts where use of a binary prefix makes sense, in order to protect the unambiguous decimal meaning of the "mega" prefix. The binary unit is in wide use by the consumer software industry, but use of the "mebi-" prefix is not. This leads to confusion where 2²⁰ (1,048,576) bytes is displayed as 1 MB instead of 1 MiB. For example, the operating system Windows XP will show a file of 2²⁰ bytes as "1.00 MB" in its file properties dialog. Likewise, a file of 10⁶ (1,000,000) bytes is reported as "976 KB".

See also

• Megabyte
• Mebibit
• Kibibyte
• Gibibyte
• Binary prefix
• SI prefix
• IEEE 1541
• Orders of magnitude (data)

External links

• NIST Prefixes for binary multiples
• IEC Prefixes for binary multiples