MB versus MiB: why two file-size numbers differ

A file can appear to have one size in a storage service and another in a desktop file manager. The bytes have not changed. The labels may use different multiplication rules.

Decimal and binary prefixes

One decimal megabyte, MB, is 1,000,000 bytes. One binary mebibyte, MiB, is 1,048,576 bytes, which is 1,024 × 1,024. Likewise, a decimal GB is 1,000,000,000 bytes while a GiB is 1,073,741,824 bytes. An application that displays “MB” while actually calculating MiB adds confusion, so look for its own definition.

Use the data storage converter to compare the units. Select MB (decimal) as the source and MiB (binary) as the destination. One thousand MB becomes about 953.674 MiB. The calculator also includes bits: eight bits equal one byte. Network speeds commonly use bits per second, whereas file sizes commonly use bytes.

Apply the difference to a real task

If an upload form allows a “10 MB” file, check whether the provider means 10,000,000 bytes or 10 × 1,048,576 bytes. The difference can determine whether an attachment is accepted. A storage device’s advertised capacity also does not equal usable capacity after formatting, file-system structures, or reserved space.

What the converter can tell you

The converter translates units mathematically; it cannot inspect a file, measure available storage, or predict transfer time. Keep the actual byte count when it is available, and state the unit convention when sharing a size estimate. Your entered number stays in the browser.