Slack File Size Limit and Teams Limits: Shrink Any File on a Mac

Slack lets you add files up to 1 GB each. Its help page also says you can drag and drop up to 10 files into the message field on desktop. It gives no separate limit for video, so a clip falls under the same 1 GB.

That cap is generous, so a failed Slack upload is often something else. The Slack Help Center page says files are checked for malware and are not uploaded if any is detected. It also lists preview limits: an image previews inline only if it is under 25,000 pixels on the longest side and under 45 million pixels total, and Office files over 50 MB show no preview. A file with no preview is still shared; people just have to download it. In Slack Connect conversations, some file types cannot be added at all, per the same page.

The Teams chat table on Microsoft’s limits page lists a file size limitation of 100 MB and 10 file attachments, with an error message if you exceed the count. Files you put in a team channel are stored in SharePoint, whose limits page lists a 250 GB file upload limit.

All figures read 11 October 2026. Microsoft dated the Teams page July 2026. If an upload fails below these numbers, see the failure causes further down.

Lower the resolution and raise the compression, in that order, then check the file size. A 1080p screen recording rarely needs more than 1080p, and a thread viewer rarely needs 4K. Smol has no “make this 100 MB” control for video, so you set quality and resolution, look at the result, and run again if it is still over.

H.265 is Smol’s default codec, but H.264 is the safer pick for chat because the person who opens it may be on any device. Our H.265 versus H.264 guide explains the trade. For the numbers behind the quality labels, see how to compress a video on a Mac, which picks CRF 26 to 28 for anything headed to Slack, and the screen recording guide if that is what you recorded. Sending the clip on a phone instead? See WhatsApp video size, or Zoom recordings for meeting captures.

Why does Slack say the upload failed under 1 GB?

A slack upload failed message under the cap usually points elsewhere: a flaky connection, a blocked file type in Slack Connect, or malware scanning. Shrinking the file helps with the first, since a smaller file survives a bad connection more often. It cannot fix a blocked file type.

Drop the file in Smol, pick MP4 and H.264, lower the resolution, run it, and read the size. The same steps work for Slack. The whole thing takes a minute or two for a short clip.

1. 1

   Drag the file or folder into Smol

   Mixed batches are fine: a video, a PDF and a screenshot can go in together.

2. 2

   Choose Compress, then MP4 with H.264

   Set the quality label to Web, or an exact CRF if you want to tune it. Reduce the resolution for long clips.

3. 3

   Run it and read the output size

   Smol shows before and after for every file and writes a copy with a _compressed suffix. By default the original is untouched.

4. 4

   Still over the cap? Lower resolution or raise CRF, and run again

   Run from the original, not the copy, so you do not stack losses.

5. 5

   Attach the compressed copy

   If Teams still refuses it, count the attachments; the chat limit is 10.

For a PDF, use the Small preset; use Medium for scanned pages. Presets are pixel caps on the long edge, 600, 900, 1200, 1800 and 2400 pixels for Tiny, Small, Medium, Large and Original, so the sharpness you get depends on the page size. Original is not lossless.

Our PDF too big to upload guide and the five PDF methods, tested have the measured results. For images, the benchmark page has the data: on 24 small 768 × 512 test photos, Smol’s AVIF needed 22 to 26% fewer bytes than the best JPEG at the same SSIMULACRA2 score. Those are small film photographs, so camera files will behave differently. Check what a tool can open on the other end before choosing AVIF for a chat; JPG or WebP is the safer pick.

More on the video side in the HandBrake alternatives comparison, and for the chat-adjacent limit see Discord’s upload limit.

Smol will not solve everything on this page. Skip it in these cases.

• You are on Windows, Linux or a phone. Smol is a Mac app and runs only on macOS.
• The file is already under the cap and the upload still fails. That points to a connection, a blocked file type or malware scanning, not size.
• You need a file to hit an exact byte count. Smol sets quality and resolution; for video it has no size target, so you must check and rerun.
• The recipient can open a link. Sharing from SharePoint or OneDrive avoids the cap and keeps one copy.
• You need to redact, edit or sign a PDF. Smol does not do that.

If your work is the opposite, a team of Macs that sends large files all day, see the pricing page: Solo is $29 for one Mac, Team is $49 for three, and Enterprise is $20 a seat from 5 seats. Presets live on each Mac, so write your settings down and recreate them.