IT
Omnvert

Reduce an STL to send by email

Gmail caps attachments at 25 MB and Outlook.com at 20 MB, and email encodes attachments in base64, which adds about 33 percent. So a file has to be under roughly 18 MB for Gmail and 15 MB for Outlook to go through as an attachment. The reducer opens here at 17 MB.

📉
Drop an STL file here or click to browse
Up to 300 MB · .stl only
Choose STL file
1
Upload STL
2
Set target MB
3
Download
MB
1 MB500 MB

We aim for exactly this size. Quality-preserving quadric decimation stops as soon as the file fits. If the mesh cannot be reduced further without breaking, we return the smallest safe result.

Pick an STL file to continue.
🔒 Files are processed on our server in isolated memory and removed within 15 minutes of your download.

EnglishTürkçe

The limit: Email

File size cap
25 MB
Triangle cap
no fixed cap
Triangles at that size
524,286

This page opens the reducer at 17 MB. Source: Gmail and Outlook attachment limits (checked 2026-09).

Why the file is over it

The STL that has to be emailed is usually the one a print shop, a client or a teacher asked for, exported straight from the design tool. Few people know that an ASCII STL is five times the size of the same mesh in binary, and fewer that the mail server measures the encoded size, not the file on disk. Both surprises show up as a bounce.

How to get under it

  1. 1Drop the STL below. The target is preset to 17 MB; use 14 MB if the recipient is on Outlook.
  2. 2Press Reduce. If the file was ASCII, converting to binary alone may reach the target with no triangles removed; the result card will say so.
  3. 3Download the reduced file and attach it. No zip is needed; STL barely compresses anyway.
Reduce for email (target 17 MB)

What to expect

A 48 MB binary STL (one million triangles) to 17 MB keeps 355,000 triangles, which is more than a 0.2 mm FDM print of a hand-sized part can show. A 48 MB ASCII STL is only about 200,000 triangles and converts to 10 MB with nothing removed.

Other ways

Google Drive and OneDrive links sidestep the limit and are the right answer for files that must stay at full resolution. For a print-ready file, a reduced attachment is simpler for the recipient and does not expire.

Questions

Why did my 22 MB file bounce from Gmail?

Base64 encoding: 22 MB on disk becomes about 29 MB in the message, over the 25 MB cap. Under 18 MB on disk is the practical limit.

Does zipping help?

Binary STL shrinks 10 to 20 percent in a zip; ASCII STL shrinks a lot more, but converting it to binary shrinks it more still and keeps it openable everywhere.

Will the recipient's slicer accept the reduced file?

Yes. The output is a standard binary STL; every slicer and CAD tool reads it.