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Attachment size checker
Pick your files and see whether they fit Gmail's and Outlook's limits once email encoding is counted. Your files are never uploaded.
You just approve.
The short version
- The checker reads file names and sizes only, in your browser.
- Email encoding makes attachments about 37% larger on the wire, so a file under the limit can still be rejected.
- Limits come from Google and Microsoft help pages, linked next to each figure.
Your files never leave this page. The checker reads each file’s name and size only, so nothing is uploaded and no content is opened.
Total
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No files chosen yet.
- Gmail (personal): 25 MBTotal attachment size. Larger files become Google Drive links. Gmail Help: attachment size limits
- Outlook.com: 25 MBThe whole email, including text and inserted and attached files. OneDrive links do not count. Microsoft: Unable to attach files in Outlook.com
- Outlook app, internet email accounts: 20 MBAttachment plus the email itself, set by the Outlook app. Microsoft: Reduce attachment size to send large files with Outlook
- Outlook app, Exchange accounts (default): 10 MBDefault for Exchange accounts in the Outlook app; admins can change it. Microsoft: Reduce attachment size to send large files with Outlook
- Microsoft 365 / Exchange Online (default): 35 MBDefault maximum message size when sending. Administrators can set 1 MB to 150 MB. Microsoft: Exchange Online limits
Here 1 MB is 1,000,000 bytes, so a file is never shown as smaller than it is. Some systems show sizes in 1,048,576-byte units, which read a little lower.
How it works
You choose files with the file picker. The page reads each file's name and size from your browser and adds them up. It does not open, read or upload the files, so there is no server involved and nothing to delete afterwards.
It then compares the total with each limit the providers publish, and with a limit of your own if you enter one.
Why a file under the limit can still bounce
Email carries attachments as text. Base64 turns every 3 bytes into 4 characters, as RFC 2045 describes, and MIME wraps lines at 76 characters. Together that adds about 37% to a file's size. Microsoft documents a 33% increase for messages that travel outside its datacenters, and gives 150 MB as the in-network ceiling and 112 MB as the ceiling after that increase.
Providers do not all say whether their figure counts the raw files or the encoded message. The checker therefore shows both: Fits when even the encoded size is under the limit, Close when only the raw size is, and Too large when the files alone exceed it.
The limits it uses
- Gmail, personal accounts: 25 MB. For work and school accounts, a Google Workspace administrator sets the limits. Gmail turns attachments over the limit into Google Drive links.
- Outlook.com: 25 MB for the whole email, text and files together. OneDrive links do not count, and a linked file can be up to 2 GB.
- Outlook app, internet email accounts: 20 MB, and 10 MB by default for Exchange accounts. Both count the attachment and the email.
- Microsoft 365 and Exchange Online: 35 MB by default when sending, which an administrator can set between 1 MB and 150 MB.
Each figure links to the page it comes from. These pages change, so check them if the number matters.
If your files are too large
Send a link instead. Gmail can attach a Google Drive link and Outlook.com can attach a OneDrive link. You can also compress the files into one archive, though already-compressed formats such as JPEG and MP4 shrink little.
Questions, answered
What is Gmail's attachment size limit?
Google's help page says the limit is 25 MB for personal Gmail accounts. For work and school accounts, a Google Workspace administrator sets the limits. Over the limit, Gmail adds the file as a Google Drive link.
Why was a 24 MB file rejected under a 25 MB limit?
Email encoding adds about 37% to an attachment's size, so a 24 MB file travels as roughly 33 MB. Providers differ on whether the limit counts the raw files or the encoded message, so leave headroom.
Why do Outlook limits show as 10, 20, 25 and 35 MB?
Microsoft publishes different figures for different things: 20 MB for internet accounts and 10 MB for Exchange accounts in the Outlook app, 25 MB for Outlook.com, and 35 MB as the default for Exchange Online. Which one applies depends on your account and client.
Does the checker upload my files?
No. It reads each file's name and size in your browser and never opens or sends the file.
And the rest of the inbox
Otto reads what arrived across Gmail and Outlook, drafts the replies, books the time and keeps track of what you are still owed. It prepares each one and waits for you to approve it.
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