> Quick answer: Slack GIF emojis must be exactly 128×128 pixels and under 128KB in file size. Animated GIFs are allowed for custom emojis but must meet these strict size limits. AnimGifMoji automatically resizes and compresses any GIF to meet Slack's requirements — free, no account needed, no files stored.
Understanding Slack GIF Size Requirements
If you've ever tried to upload a GIF as a custom emoji in Slack and hit an error, the file size or dimensions were almost certainly the problem. Slack enforces strict limits on custom emoji files, and GIFs are no exception.
Here are the exact Slack GIF size requirements you need to know:
| Requirement | Limit |
|---|---|
| Maximum dimensions | 128×128 pixels |
| Maximum file size | 128KB |
| Supported formats | PNG, JPG, GIF |
| Animated support | Yes (GIF only) |
These limits apply to custom emojis — the ones you upload to your Slack workspace under Customize → Emoji. If you're sharing a GIF in a message (not as an emoji), Slack has different, more generous limits (up to 1GB for file uploads).
Understanding the difference is key: when people search for "Slack GIF size," they usually want one of two things — either how to size a GIF for use as a custom emoji, or what the limits are for sharing GIFs in messages. This guide covers both.
> 💡 Tip: Always check your GIF dimensions AND file size before uploading to Slack. A GIF can be the right pixel size but still fail if the file is over 128KB — Slack will silently reject it or show a vague error.
Slack Custom Emoji GIF Size: The 128×128 Rule
The 128×128 pixel limit is Slack's hardcoded maximum for custom emojis. It applies to all formats — PNG, JPG, and GIF alike. If your GIF is larger than 128×128, Slack will either reject it or automatically downscale it (often with poor quality results).
Why 128×128? This is a common standard across chat platforms for emoji-sized graphics. It's large enough to be recognizable in the chat interface but small enough to render quickly without impacting performance. Discord uses the same 128×128 standard, though with a more generous 256KB file size limit.
What Happens If Your GIF Is Too Large?
If you try to upload a GIF that exceeds Slack's limits, you'll typically see one of these outcomes:
- Slack rejects the upload with an error message like "File too large" or "Invalid file type"
- Slack auto-resizes the image but only for static images — animated GIFs often lose their animation in this process
- The animation stops working — you upload the file successfully, but the emoji appears as a static image because the file was too large to animate
The safest approach is to resize and compress your GIF before uploading it to Slack. Tools like AnimGifMoji handle this automatically.
Slack GIF Size for Message Sharing vs. Custom Emojis
People searching for "Slack GIF size" often mean different things. Here's the breakdown:
Custom Emoji GIFs (Strict Limits)
- Max dimensions: 128×128px
- Max file size: 128KB
- Purpose: Create
:custom-emoji:shortcuts for your workspace - Who can add: Workspace members with permission (default: everyone)
GIFs Shared in Messages (Generous Limits)
- Max file size: 1GB (for direct file uploads)
- Via Giphy integration: No size limit (Slack hosts the GIF)
- Purpose: Share animated GIFs in conversations
- Who can share: Any workspace member
If you're just sharing a GIF in a Slack channel message, you don't need to worry about the 128×128 limit. You can drag-and-drop a GIF file directly into the message composer, or use the /giphy slash command to search and share GIFs from Giphy's library.
The strict 128×128/128KB limits only apply to custom emoji uploads.
> ⚠️ Warning: Slack's Giphy integration only works if your workspace admin has enabled it. If /giphy isn't working, check with your admin or use a direct file upload instead.
How to Resize a GIF for Slack Custom Emoji
Getting your GIF to meet Slack's requirements involves two steps: resizing to 128×128 pixels and compressing the file under 128KB. Both steps need to happen — and neither one alone guarantees the other.
Using AnimGifMoji (Recommended)
AnimGifMoji is a free online tool purpose-built for converting GIFs to platform-specific emoji sizes. It handles both resizing and compression automatically.
- Go to AnimGifMoji at animgifmoji.com
- Drag and drop your GIF onto the upload area
- Select "Slack" as the target platform
- AnimGifMoji automatically resizes to 128×128px and compresses under 128KB
- Download your resized, compressed GIF
- Upload to Slack: Go to your workspace → Customize → Emoji → Add Custom Emoji
The tool preserves the GIF animation while meeting Slack's size constraints — it won't strip the animation like some image editors do when they compress files aggressively.
> ✅ Pro tip: If your GIF has many frames or a long duration, AnimGifMoji may reduce the frame rate slightly to hit the 128KB target. For the best quality results, start with a GIF that's already under 5 seconds long.
Manual Resizing Options
If you prefer a manual approach, here are the tools you can use:
For resizing (dimensions):
- Adobe Photoshop: File → Export → Save for Web (choose GIF, set width/height to 128)
- GIMP: Image → Scale Image → 128×128, then export as GIF
- Ezgif.com: Upload GIF, use the "Resize" tool, set to 128×128
For compression (file size):
- Ezgif.com Optimizer: Reduces GIF file size by removing frames or reducing colors
- ILoveIMG GIF Compressor: Web-based, supports batch compression
- Photoshop Save for Web: Reduce colors (256 → 64 or fewer) to shrink file size
The challenge with manual tools is that you often have to do resizing and compression in two separate steps, and it's easy to end up with a file that looks great at 128×128 but is still 200KB — which Slack will reject.
Slack GIF Size Requirements vs. Other Platforms
If you use emoji GIFs across multiple platforms, here's how Slack compares:
| Platform | Max Dimensions | Max File Size | Animated GIFs | Notes |
|---|---|---|---|---|
| Slack | 128×128px | 128KB | Yes | Custom emoji only |
| Discord | 128×128px | 256KB | Nitro required* | Server emoji uploads free |
| Microsoft Teams | 128×128px | 1MB | Yes | Via Teams app store or upload |
| 512×512px | 500KB | Yes (stickers) | WAWebp format required |
*Discord animated emojis from other servers require Nitro, but you can upload animated GIFs as custom emojis to your own server for free.
Slack has the tightest file size limit at 128KB. Discord gives you twice as much headroom at 256KB, and Teams is even more generous at 1MB. If you're creating emoji GIFs that need to work across Slack, Discord, and Teams, optimizing for Slack's limits will ensure compatibility everywhere.
For cross-platform emoji GIFs, see our guides on converting GIFs to Discord emoji and Microsoft Teams animated emoji.
Why Slack's 128KB Limit Is Strict (And How to Work Within It)
128KB sounds small, but most short animated GIFs can be compressed to fit within this limit without losing visible quality. Here's why the limit exists and how to work with it effectively.
Why 128KB?
Slack loads emojis in every message where they're used. If a custom emoji is 1MB, and 20 people use it in a channel, Slack needs to load 20MB of emoji data just for that one emoji. The 128KB limit keeps emoji-heavy channels from becoming slow to load.
This is especially important in large Slack workspaces with hundreds of members and dozens of active channels. Slack's performance would degrade significantly without file size limits on frequently-used assets.
How to Keep Quality High Within 128KB
GIF file size depends on three factors:
- Dimensions — smaller = smaller file size (128×128 is already helping)
- Number of colors — reduce from 256 to 64 or fewer if needed
- Number of frames — fewer frames = smaller file, but less smooth animation
- Duration — shorter GIFs have fewer frames and smaller file sizes
For best results with Slack emojis:
- Keep the animation under 3 seconds
- Use GIFs with solid color areas rather than photorealistic images (photos don't compress as well)
- Accept a slight reduction in frame rate if needed — 15fps looks smooth enough for emoji use
> ℹ️ Did you know? Animated GIF emojis in Slack are one of the most effective ways to add personality to a workspace. Workspaces that use custom animated emojis report higher engagement in channels — teammates are more likely to react and respond when they have fun, expressive emoji options.
How to Add a GIF Emoji to Slack: Step-by-Step
Once you have a properly sized GIF (128×128px, under 128KB), here's exactly how to add it as a custom emoji in Slack:
Desktop (Slack App or Web)
- Open your Slack workspace in the desktop app or at slack.com
- Click your workspace name at the top left
- Select "Customize [Workspace Name]" from the dropdown
- Go to the "Emoji" tab
- Click "Add Custom Emoji"
- Upload your GIF file — it must be 128×128px and under 128KB
- Give it a name (this becomes the
:emoji-name:shortcut) - Click "Save"
The emoji is available immediately to everyone in the workspace.
Mobile (Slack iOS/Android)
Custom emoji management is only available in the desktop app or web browser. You can't add custom emojis from the Slack mobile app — you can only use emojis that have already been added.
Once an animated GIF emoji is added via desktop, it animates on mobile too.
Troubleshooting: Why Is My GIF Not Working in Slack?
If your GIF emoji isn't working as expected, here are the most common causes and fixes:
Problem: Upload fails with "file too large" error Fix: Compress your GIF further. Target under 100KB to have a safe margin below the 128KB limit. Use AnimGifMoji or Ezgif.com optimizer.
Problem: Emoji uploads but appears as a static image Fix: Your GIF's animation was likely stripped during compression. Use a tool that preserves GIF animation frames, like AnimGifMoji — it compresses the file size without stripping the animation.
Problem: Emoji looks blurry or pixelated Fix: Slack is probably scaling down a GIF that's not exactly 128×128. Resize to exactly 128×128px before uploading.
Problem: Emoji name is already taken Fix: Choose a unique name. Slack doesn't allow two emojis with the same name, even if an old one was deleted (the name stays reserved).
Problem: No option to add custom emoji Fix: Your workspace admin may have disabled custom emoji uploads for regular members. Contact your Slack workspace admin to request permission.
Related Articles
- Animated Emoji GIF — How to Make and Use Them
- Slack Emoji GIF — Complete Setup Guide
- How to Add a GIF Emoji to Slack
- Convert GIF to Slack Emoji — Quick Guide
- Slack Emoji Size Guide
Frequently Asked Questions
What is the maximum GIF size for Slack emoji?
Slack custom emoji GIFs must be a maximum of 128×128 pixels in dimensions and under 128KB in file size. Animated GIFs are supported for custom emojis, but both limits must be met for the upload to succeed.
Can I upload animated GIFs to Slack?
Yes, you can upload animated GIFs as custom emojis in Slack. The GIF must be 128×128 pixels or smaller and under 128KB in file size. AnimGifMoji can automatically resize and compress your GIF to meet these requirements.
Why does my GIF look blurry after uploading to Slack?
If your GIF looks blurry in Slack, it's likely because the file was larger than 128×128px and Slack auto-scaled it. Always resize your GIF to exactly 128×128px before uploading to get crisp, clear results.
Does Slack support animated emoji GIFs?
Yes, Slack supports animated GIF emojis. When you upload a GIF as a custom emoji, it animates in the chat interface. The animation must be contained in a GIF file that's under 128KB — larger files may be accepted but the animation may not play.
How do I make a GIF smaller for Slack?
To make a GIF smaller for Slack, use AnimGifMoji at animgifmoji.com — it automatically resizes to 128×128px and compresses under 128KB. You can also use Ezgif.com's optimizer to reduce frames and colors manually.