Convert megabytes to mebibytes

A megabyte (MB) is one million bytes, or 10⁶ B, like every other unit with the SI prefix mega. A mebibyte (MiB) is 2²⁰ bytes, or 1,048,576 B. The IEC named it so that a size counted in powers of two would stop sharing a name with the decimal one; before that, 1,048,576 bytes was also commonly called a megabyte[1].

A mebibyte is 4.86% larger than a megabyte. For a photo from your phone that is a fraction of a megabyte, but for a 1,000 MB video it is already more than 46 units, because the same video is 953.67 MiB.

The gap grows with larger sizes, as the GB to GiB converter shows, and the data size converter handles any other pair of units.

Multiply the megabytes by one million to get bytes, then divide by 1,048,576. In one step: MiB = MB × 0.95367431640625. The factor is exact, because a million divided by 2²⁰ ends after fourteen decimal places.

A 25 MB attachment is 25 × 0.95367 = 23.84 MiB, and a 700 MB disc image is 667.57 MiB. The result always comes out about 4.6% lower than the number in megabytes.

In Excel, use =CONVERT(A2,"Mbyte","Mibyte"). In this function "Mi" stands for mebi, 2²⁰, and plain "M" for mega[2].

The MiB to MB converter goes the other way, and the Swap order button carries your result over.

macOS reports file sizes in decimal megabytes, while Windows divides the byte count by powers of 1024 and still labels the result MB[3]. A file that Finder lists as 100 MB therefore shows 95.4 MB in File Explorer, without losing a single byte.

Upload limits work the same way. USCIS, the US immigration agency, accepts evidence uploaded with a form filed through its website only up to 12 MB per file[4]. If that limit is counted in decimal, a scan that Windows lists as 11.5 MB is really 12.06 MB and goes over it. In that case, run the Windows figure through the MiB to MB converter.