Guides / MB vs MiB: what your upload limit really means

MB vs MiB: what your upload limit really means

A 10 MB limit and a 10 MiB limit differ by nearly half a megabyte. If your files sit in between, it decides whether the upload works.

The two definitions

• 1 MB (megabyte) = 1,000,000 bytes.
• 1 MiB (mebibyte) = 1,048,576 bytes.

So 10 MB is 10,000,000 bytes and 10 MiB is 10,485,760 bytes, a difference of 485,760 bytes (about 4.9%).

Which one does the portal use?

Many websites write “MB” but check against 1,048,576. Others check against 1,000,000. Operating systems also differ in how they display sizes. If the portal does not say, assume the stricter one: MB.

Plan with a margin

Aim for a total at least 1–2% under the limit. FileMending lets you enter the limit in MB, MiB or KB and keeps a safety margin by default, and it shows the exact byte total so you can compare against the portal's wording.

Frequently asked questions

Is 10 MB the same as 10 MiB?

No. 10 MB is 10,000,000 bytes; 10 MiB is 10,485,760 bytes.

Which should I choose if unsure?

Choose MB. It is the smaller number, so files that fit it also fit the MiB reading.

Updated 2026-10-12. General information, not legal advice. Always check the requirements of the portal or office you are uploading to.