Slack Emoji: How to Add, Size, and Use Custom Emoji

This is an independent guide. Not affiliated with or endorsed by Slack Technologies, LLC or Salesforce, Inc.

Slack ships with thousands of built-in emoji, but the real personality of a workspace comes from the custom ones your team uploads. A well-chosen custom emoji can replace a five-word reply, celebrate a deploy, or become the inside joke that holds a remote team together.

This guide covers everything about Slack emoji: how to create and upload them, the exact size and format requirements, how emoji reactions work, and tips for keeping your emoji library useful instead of chaotic. Whether you're adding your first custom emoji or cleaning up a workspace with 3,000 of them, you'll find what you need here.

If you're new to Slack entirely, start with our what is Slack overview first.

Slack Emoji Size and Format Requirements

Getting the size right matters. An emoji that looks crisp in the picker but blurry in a message (or one that's too large to upload) wastes everyone's time.

Recommended dimensions: 128 x 128 pixels. Slack will resize larger images down, but starting at 128x128 gives you the sharpest result at the size Slack actually displays emoji.

Maximum file size: 128 KB. If your image is too large, reduce the resolution or compress it. For PNGs, tools like TinyPNG can cut file size significantly without visible quality loss.

Supported formats: PNG, GIF, and JPG. Use PNG for images that need transparent backgrounds (logos, icons, cutout faces). Use GIF for animated emoji. JPG works but doesn't support transparency.

Shape: Square works best. Non-square images will be squished into a square frame, which usually looks awkward. If your source image isn't square, add transparent padding around it to make it square before uploading.

Transparent backgrounds: Use PNG format if you want the emoji to blend into messages without a white box around it. This is especially important for emoji that sit inline with text.

Jordan manages a 60-person design agency. She created a shared Figma template at exactly 128x128 pixels with alignment guides. When anyone on the team wants to make a new emoji, they start from the template. Every emoji in their workspace looks consistent, and nobody wastes time troubleshooting upload errors.

Quick reference:

How to Use Emoji Reactions in Slack

Emoji reactions are one of Slack's most useful features. Instead of cluttering a channel with "got it" or "looks good" messages, you react to a message with an emoji. It keeps conversations clean and still gives the sender feedback.

Adding a reaction: Hover over any message, click the smiley face icon that appears, and pick an emoji. You can also use the keyboard shortcut: press +: then start typing the emoji name.

Reacji for workflows: Slack's Workflow Builder can trigger automations based on emoji reactions. For example, reacting with a :ticket: emoji could automatically create a support ticket, or a :approved: reaction could move a request to the next stage. Teams use this to build lightweight approval workflows without any code.

Emoji polls: Need a quick decision? Post a message like "Where should we do the offsite?" and add location emoji as reactions. Team members click the one they prefer. It's not a formal poll tool, but it works well for fast, informal votes.

Sam leads a support team of 12. They use a :eyes: reaction to claim a customer issue ("I'm looking at this"), :white_check_mark: when it's resolved, and :sos: when they need help. New hires learn the system in five minutes, and the channel stays readable even during busy hours.

Tips for reactions:

• Establish team conventions for common reactions (acknowledged, approved, needs discussion)
• Use custom emoji for team-specific statuses that standard emoji don't cover
• Remember that reactions are visible to everyone in the channel

Best Practices for Custom Slack Emoji

A workspace with good emoji culture is fun to use. A workspace with 4,000 unlabeled emoji that nobody can find is not. Here are practices that keep things useful.

Use consistent naming conventions. Prefix related emoji with a category: :team-alice:, :team-bob: for team member faces; :status-wfh:, :status-ooo: for availability statuses; :flag-us:, :flag-de: for country flags. Prefixes make emoji searchable by group.

Organize by category. When people can type :team- and see all team faces autocomplete, the emoji library becomes genuinely useful rather than a junk drawer.

Don't overdo it. A few hundred well-chosen emoji serve a team better than thousands of random ones. Periodically review and remove emoji that nobody uses. Slack admins can see usage data on the customization page.

Think about accessibility. Emoji add personality, but don't rely on them as the only way to communicate something important. Not everyone processes visual symbols the same way, and screen readers may not convey the intended meaning of a custom emoji. Pair important emoji with text.

Respect the workspace. Avoid uploading emoji that could be offensive or exclusionary. What seems funny to one person might make a colleague uncomfortable. When in doubt, skip it.

Keep file sizes small. Large, uncompressed images slow down the emoji picker and waste storage. Compress images before uploading.

For more ways to get the most out of Slack, see our Slack tips and tricks guide, or explore our overview of how to use Slack effectively.

Where to Find Custom Slack Emoji

You don't have to make every emoji from scratch. There are several good sources for ready-made custom emoji.

Slackmojis.com: The most popular free library of Slack-ready emoji. Thousands of animated and static emoji, pre-sized and ready to upload. Categories include parrots, reactions, memes, and tech logos.

Make your own: Tools like Figma, Canva, or even Preview (on Mac) can create 128x128 pixel images quickly. For animated emoji, use a GIF editor or convert short video clips into small GIFs. Keep the animation simple since complex GIFs often exceed the 128 KB limit.

Team-specific emoji: The most valuable custom emoji are often the ones unique to your team. Team member faces, project logos, inside jokes, and company values turned into small icons all build a sense of shared identity. Ask your team what emoji they wish existed, and you'll get surprisingly creative suggestions.

AI image generators: Tools like DALL-E or Midjourney can generate small icons and illustrations. Generate an image, crop it to 128x128 pixels, compress it under 128 KB, and upload. This is a fast way to create unique emoji when you need something specific but don't want to design it by hand.

Slack is a trademark of Slack Technologies, LLC, a Salesforce company. This site is not affiliated with, endorsed by, or sponsored by Slack Technologies, LLC or Salesforce, Inc.

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