Slack GIF Size: The 128 KB Emoji Limit and File Uploads
There are two Slack limits that people mix up. One is the size of a file you share in a message, which is generous. The other is the size of a custom emoji, which is tiny, and which is the one that eats animated GIFs for breakfast. This guide is mostly about the second.
Why animated emoji fail
The size limit is brutal for animation. Every frame is a full picture, and 128 KB disappears fast: a long loop, too many frames, or a detailed image will push it over. The fix is the same three things every time. Keep it to a second or two. Keep the frame rate low. Keep the picture simple.
| Length | Best | Balanced | Smallest |
|---|---|---|---|
| 1 second | 21 KB | 17 KB | 13 KB |
| 2 seconds | 37 KB | 28 KB | 19 KB |
On this simple test clip even the best quality is comfortably inside 128 KB. Real footage is busier, so expect to use more of the allowance, and expect to need the lower quality settings.
A recipe that works
- Add a clip or an animation and trim it to one or two seconds.
- Use the crop tool and choose 1:1 so the emoji is square.
- On the Format tab set the width to 128 px and the frame rate to 10 fps.
- Under "Size to fit" choose 128 KB · Slack emoji and press Fit to 128 KB. If it can't fit, it tells you how many seconds you can keep.
- Download the GIF and upload it in Slack's emoji settings.
Sharing files in messages
For a normal message you can attach much larger files, so a GIF isn't going to hit a hard limit the way an emoji does. The practical limit is people's patience: a 20 MB GIF is slow for everyone to load. Shorter and smaller is still kinder, and an MP4 is often the better choice when it doesn't need to loop as an image.
Shrink a GIF for a messageLower the width or frame rate and check the estimate before you convert.