How to make a Slack emoji GIF under 128 KB
1 min read
Slack lets you add animated GIFs as custom emoji, but the limit is tight: 128 KB. Most reaction GIFs from the web are several megabytes, so they need to be resized and compressed first.
Slack emoji requirements
| Requirement | Value |
|---|---|
| Max file size | 128 KB |
| Recommended dimensions | Square, about 128×128 px |
| Formats | GIF, JPG, PNG |
Checked November 2026. See Slack’s help center for the latest rules.
Step by step
- Open GifSmaller — the Slack emoji goal is preselected.
- Drop your GIF. GifSmaller resizes it to 128 px and compresses it until it is under 128 KB.
- Download the result.
- In Slack, open Customize workspace → Emoji → Add custom emoji, upload the GIF and give it a name.
Tips for a crisp emoji
- Crop to a square first. Emoji are shown in a square; extra width becomes empty space.
- Fewer frames help. If the result is still over 128 KB, shorten the loop before compressing.
- Simple beats detailed. Bold shapes and flat colors survive compression far better than photos.
If the target cannot be reached, GifSmaller tells you the smallest size it managed, so you know to trim the GIF rather than guessing.
Try it on your GIF
Compress it in your browser. Free, and nothing is uploaded.
Open the compressor