I am getting rejection on my 13.5MB attachment even though size limit is 15MB. So, I want to know the exact policy by Gmail, as in how do they calculate the size of an email which contains attachment?

1 Answer 1


The 15MB limit is for the entire message, not just attachments.

To check the size of a message, open it, and select Show Original from the menu in the upper right. This opens the entire message in a new tab/window. Save this to a plain text file and the size of that file is the total size of the message.

Tl;dr: If Gmail says your message is too big, you'll have to make it smaller. Try sharing the file via Drive or Dropbox and emailing a link.

  • 3
    That was helpful, thank you. I also got some info from other sources. Got answers like gmail uses Base64 encoding which automatically adds its own data. You should always keep the buffer of 33% to ensure guaranteed delivery.
    – Shearce
    Jul 12, 2016 at 4:18

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