Slack emoji size limits: 128×128px, 128KB, GIF/PNG
2026-09-08
Slack custom emoji have three limits. Meet them and uploads never fail.
| Limit | Value |
|---|---|
| Format | GIF, PNG, JPG |
| Dimensions | resized to 128×128px |
| File size | under 128KB |
Dimensions: 128×128px
Slack scales the longer side to 128px, so a 512px PNG uploads fine. Two things to keep in mind:
- Emoji render at about 22px inline and 16px as reactions. Text and fine detail turn to mush, so simple, large shapes work best.
- Non-square images keep their ratio. A 220×93 GIF becomes 128×54 and looks small. Crop to a square if it matters.
File size: under 128KB
This is the limit people actually hit, especially with animated GIFs, where every frame is a full image.
- PNG/JPG: usually fine even over 128KB, because resizing shrinks them.
- GIF: Slack does not recompress frames, so the original must be under 128KB. Otherwise it is rejected or saved as a still image.
GIF size scales with dimensions × frames × colors. How to reduce each is in Shrink a GIF to under 128KB.
Format: GIF, PNG, JPG
- Only GIF animates. APNG, WebP and MP4 are not accepted.
- Transparency works in PNG and GIF. If your team uses dark mode, transparent backgrounds look far better.
Name rules
- lowercase letters, numbers,
-,_ - no spaces, uppercase or non-ASCII
- cannot collide with standard emoji names (
:smile:etc.)
Files on this site
Every emoji here is converted to:
- longest side 128px or less
- under 128KB (GIFs have frames and colors reduced step by step)
- file name equals the emoji name (
rollback.gif→:rollback:)
Download and upload as-is. Steps are in How to add custom emoji to Slack.
FAQ
What is the maximum file size for a Slack emoji?
128KB. PNG and JPG files over that are often shrunk automatically, but a GIF over 128KB is rejected or loses its animation, so shrink it first.
Does the image have to be square?
No. Slack scales the longer side to 128px and keeps the aspect ratio. Square images look bigger in chat, though.
Are SVG or WebP supported?
No. Only GIF, PNG and JPG.