Slack GIF Size Limit: 1 GB in Messages, 128 KB for Emoji (Tested)

The Slack GIF size limit depends on where the GIF goes. A GIF you post in a message or thread is a file, and Slack's help center says you can add files up to 1 GB, which our file size limit test measured as exactly 1,073,741,824 bytes. It plays inline if it is smaller than 25,000 pixels on its longest side and 45 million pixels in total. A GIF you upload as a custom emoji is the strict case. We tested it on 4 October with 11 GIFs: the emoji limit is 128 KB exactly (131,072 bytes) after Slack's own resize, and the 50-frame limit in Slack's help center is not enforced; an 86-frame GIF went through with every frame. When Slack says a GIF is too big, it is almost always an emoji upload.

Slack GIF limits by where the GIF goes

A GIF above the preview limits still uploads. People see it as a file to click instead of an image playing in the channel. Some workspaces also restrict which files members and guests can upload, especially in Slack Connect channels with other companies.

The steps for each way to post a GIF, from the built-in picker to uploading your own, are in how to add a GIF in Slack.

Slack GIF emoji size limit, measured

Slack's Add custom emoji dialog says "Square images under 128KB and with transparent backgrounds work best. If your image is too large, we'll try to resize it for you." To find the real limit, we uploaded GIFs to a test workspace with Slack's emoji.add call, the one the dialog uses, then downloaded what Slack stored:

The cut-off sits between 130,972 and 131,545 bytes, which is 128 KiB (131,072 bytes). Slack first shrinks a larger GIF to 128 by 128 pixels and checks the size again, so a big but simple GIF can pass while a small, busy one fails. The dialog shows the rejection like this:

The full upload steps, and who is allowed to add emoji, are in how to add custom emoji to Slack.

A 128 by 128 pixel image is the usual size. Emoji show at 32 pixels or smaller in messages, so a bigger image does not look better; it only adds bytes. Noise and photo detail cost the most bytes: our 30-frame noise GIF was 693 KB at 128 pixels, while a 60-frame cartoon-style GIF was 13 KB.

Discord allows twice as much, 256 KB per emoji. If the same GIF fails there, see Discord emoji too big.

How to shrink a GIF for Slack

The file size of a GIF comes from four things: pixel size, frame count, number of colors, and how much changes between frames. Cut them in that order:

• Crop to a square around the subject.
• Scale to 128 by 128 pixels.
• Cut frames. Drop every second frame, or trim the clip to 2 or 3 seconds. Slack does not cap the count at 50, but every frame adds bytes.
• Reduce colors from 256 to 64 or 32. Cartoon GIFs lose almost nothing.

Our Slack emoji resizer does all four in the browser: it resizes every frame, keeps 50 frames spread across the clip if the source has more, and re-encodes until the file is under 128 KB. Nothing is uploaded to a server. To make a new animated emoji instead of shrinking one, see Slack GIF creator.

If you prefer the command line, gifsicle does the same:

# Resize to 128x128, cut to 64 colors, lossy compression, optimize
gifsicle --resize 128x128 --colors 64 --lossy=80 -O3 input.gif -o emoji.gif

# Check the result is under 128 KB (131,072 bytes)
ls -l emoji.gif

To make a GIF emoji from a video clip, ffmpeg can take 3 seconds at 10 frames a second, which gives 30 frames (measured sizes for each frame rate and color count are in how to make an emoji from a video):

ffmpeg -t 3 -i clip.mp4 -vf "fps=10,scale=128:128:force_original_aspect_ratio=increase,crop=128:128,split[a][b];[a]palettegen=max_colors=64[p];[b][p]paletteuse" emoji.gif

Slack GIF too big: what the error means

A GIF that shows as a still image for one person and plays for another is usually that person's accessibility setting, not the file.

Does Slack compress GIFs?

A GIF posted as a file keeps its original file, and people can download it at full size. Our Slack image compression test found the same for PNG and MP4 files, while a JPEG came back re-encoded without its EXIF data. For emoji, do not count on Slack to shrink an oversized GIF; shrink it first so the upload goes through and the animation stays smooth. The picker GIFs come from GIPHY and load from GIPHY's servers at the size GIPHY serves.

FAQ

What is the max GIF size for Slack? 1 GB for a GIF posted as a file, per Slack's help center. For a custom emoji, 131,072 bytes after Slack resizes it to 128 by 128.

How many frames can a Slack GIF emoji have? Slack's help center says 50, but an 86-frame GIF was accepted with every frame kept in our test. The byte limit is what stops long GIFs.

What size should a Slack emoji GIF be? 128 by 128 pixels and under 128 KB.

Can I make a Slack GIF emoji bigger in messages? No. Emoji show at a fixed small size. To show a GIF large, post it as a file or use the GIF picker.