Slack Emoji Size Guide (2026)

Slack is used by over 79 million people every month across 750,000+ organizations. Custom emoji are a huge part of workplace culture — teams use them for reactions, inside jokes, and quick communication. But getting the technical specs wrong means blurry icons, rejected uploads, or emoji that look nothing like what you designed.

This guide covers every specification you need to create perfect Slack custom emoji in 2026, from pixel dimensions to file format choices and animated GIF limitations.

Slack Custom Emoji — Quick Specs Table

Dimensions & Display Size

Slack requires custom emoji to be 128 × 128 pixels in a square (1:1) aspect ratio. If you upload a non-square image, Slack will force it into the 128×128 frame, stretching or squishing it in the process. This is the number one cause of distorted emoji.

However, the upload size is not the display size. In Slack messages, emoji render at approximately 22–32 pixels depending on the context (inline text, reaction, or emoji picker). This means your design needs to be readable at thumbnail scale — not just at the 128px source size.

Always preview your emoji design at 28px before uploading. If you can't identify it at that size, simplify the design. Bold outlines and high contrast colors work best.

File Size Limit: Exactly 128 KB

Every Slack custom emoji — static or animated — must be under 128 KB (131,072 bytes). Slack enforces this limit strictly. Even one byte over will be rejected with no option to auto-compress.

For static PNG emoji at 128×128 pixels, staying under 128 KB is usually easy. But animated GIFs can quickly exceed this limit, especially with many frames or a large color palette. If your file is too large, reduce the number of frames, limit colors to 64 or fewer, or use our resizer tool to auto-compress.

Supported File Formats

PNG is the best choice for static emoji. It supports full alpha-channel transparency, which means smooth, anti-aliased edges that blend naturally into any Slack theme. JPEG should be avoided for emoji because it doesn't support transparency and introduces compression artifacts on small images.

GIF is required for animated emoji and is the only animated format Slack accepts. However, GIF transparency is binary — each pixel is either fully transparent or fully opaque. This creates visible jagged edges around curves and diagonal lines, unlike PNG's smooth alpha blending.

Animated Emoji: GIF Rules & Limits

Slack supports animated GIF emoji with the following constraints:

• Maximum 50 frames per GIF — exceeding this may cause Slack to reject the file or display it incorrectly
• 128 KB file size limit — the same limit as static emoji, which makes optimization critical
• 128 × 128 pixels — same dimensions as static emoji
• Users can disable auto-play — via Settings > Accessibility > "Automatically play animations"

Tips for Keeping Animated Emoji Under 128 KB

1. Reduce frames: Aim for 10–20 frames. Simple loops (bouncing, spinning, waving) look great with fewer frames.
2. Limit colors: Reduce the color palette to 32–64 colors. GIF supports up to 256, but fewer colors means smaller files.
3. Minimize motion area: Keep most of the frame static and only animate a small region. Full-frame changes create much larger files.
4. Use our tool: Our Slack Emoji Resizer automatically optimizes animated GIFs to fit within the 128 KB limit while preserving animation quality.

PNG vs GIF: The Transparency Difference

Transparency quality is the biggest visual difference between PNG and GIF emoji. This matters because Slack users can switch between light and dark themes, and your emoji needs to look good on both backgrounds.

For static emoji, always use PNG. The smooth transparency edges make a noticeable difference at small display sizes. For animated emoji, you're limited to GIF — design around the jagged edges by using solid backgrounds or thick outlines that mask the binary transparency.

Design Tips for Small Display Sizes

Remember: your 128×128 pixel emoji will display at roughly 22–32 pixels in Slack chat. Designs that look great at full size can become unrecognizable blobs at that scale. Follow these guidelines:

• Use bold outlines (2–4px at source size) — thin lines disappear at 28px
• High contrast colors — avoid subtle gradients or pastel-on-pastel combinations
• Simple shapes — one subject, one idea. No fine detail or small text
• Test at 28px — zoom out or view your design at actual display size before uploading
• Transparent background — use PNG transparency so your emoji blends naturally in chat
• Check both themes — preview against dark (#1A1D21) and light (#FFFFFF) backgrounds

Avoid placing light-colored content near the edges of transparent emoji. On Slack's light theme, light-colored edges can become invisible, making your emoji look cropped or incomplete.

How to Upload Custom Emoji to Slack

From Desktop (Windows, Mac, Linux)

1. Open your Slack workspace
2. Click the smiley face icon in the message input to open the emoji picker
3. Click "Add Emoji" in the bottom-left of the picker
4. Click "Upload Image" and select your 128×128 PNG or GIF file
5. Enter a name for your emoji (letters, numbers, and dashes only)
6. Click "Save" — your emoji is instantly available to everyone in the workspace

From iOS

1. Open the Slack app and navigate to any channel
2. Tap the emoji icon in the message field
3. Scroll right and tap the "+" button
4. Choose a photo from your camera roll, crop to square, and name it

The Slack Android app does not currently support adding custom emoji. Android users must use the desktop app or access Slack through a web browser to upload emoji.

Permissions

By default, all workspace members (except guests) can add custom emoji. Workspace Owners can restrict this permission if needed. On Enterprise Grid plans, a dedicated "Customizations Manager" role can be assigned to delegate emoji management.

Common Errors & Fixes

Frequently Asked Questions