A megabyte (MB) is a large number used when talking about hard drives or computer memory. One megabyte is 1 million bytes or 1 thousand kilobytes.

Until December 1998, when the International Electrotechnical Commission (IEC) first defined a mebibyte as 2²⁰, or 1,048,576 bytes, megabyte also meant either 1,048,576 bytes, or 1,024,000 bytes. Casual computer users still often use megabyte to mean one of these numbers.

One thousand megabytes make one gigabyte.

This definition is part of the International System of Quantities.