The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB. The unit prefix mega is a multiplier of 1,000,000 (10^{6}) in the International System of Units (SI). Therefore, one megabyte is one million bytes of information. This definition has been incorporated into the International System of Quantities.

However, in the computer and information technology fields, several other definitions are used that arose for historical reasons of convenience. A common usage has been to designate one megabyte as 1,048,576 bytes (2^{20} B), a measurement that conveniently expresses the binary multiples inherent in digital computer memory architectures. However, most standards bodies have deprecated this usage in favor of a set of binary prefixes, in which this quantity is designated by the unit mebibyte (MiB). Less common is a convention that used the megabyte to mean 1000×1024 (1,024,000) bytes.