MB vs MiB: why the same file can show different sizes
Compare the underlying byte count
NIST distinguishes decimal prefixes from binary prefixes. GB uses a billion bytes, while GiB uses 1,073,741,824 bytes. When comparing two reports, record both the number and its unit. A label alone can be ambiguous in some software, so use the exact byte count when it is available.
| Example file | Decimal display | Binary display |
|---|---|---|
| 10,000,000 bytes | 10 MB | 9.536743 MiB |
| 25,000,000 bytes | 25 MB | 23.841858 MiB |
| 1,000,000,000 bytes | 1 GB | 0.931323 GiB |
These are calculated examples, rounded to six decimal places. No compression or conversion of the file is involved.
Use the calculator
Enter a size and choose its original unit. The result is another representation of the same quantity. This tool does not inspect a file, measure free disk space, or predict how much a ZIP archive will shrink.
An upload-limit example
Imagine a form that explicitly allows 25,000,000 bytes. A file of 24,000,000 bytes is below that limit; a file of 26,000,000 bytes is above it. If your application displays MiB, converting both values into bytes gives you a common basis for comparison.
If a service only says “25 MB,” consult its own instructions rather than assuming that a rounded display guarantees acceptance. A size conversion cannot determine whether the service accepts the file type or has other requirements.
A useful note to keep
For a failed upload, record four things: the exact file size, the displayed unit, the service’s stated limit, and the error message. This makes a support request more useful than saying the file is “about 25.”
If you create a smaller copy, open it and compare the result before replacing the original. A smaller byte count is only helpful when the document or image still serves its purpose.