Slack custom emoji size and the 128KB limit

Slack custom emoji are reaction images that anyone in the workspace can add and use. Here is what PochiSta exports for Slack.

At the same 128×128px, Slack's limit is 128KB — half of what Discord allows for emoji (256KB). An image made for another platform can be rejected on file size alone.

• Slack: 128×128px / 128KB or less
• Discord: 128×128px / 256KB or less
• Twitch: 112×112px and others / animated is 1MB or less

Animated GIFs have to fit in that same 128KB budget, so frame count and color count matter more here than anywhere else.

In order of impact. These apply to both static and animated emoji.

1. Reduce the number of colors

   For simple artwork like text with an outline, reducing colors barely changes what you see. For both PNG and GIF, color count maps directly to file size.

2. Avoid gradients and photos

   Flat fills compress extremely well. At 128px you can hardly see a gradient anyway, so there is little to lose.

3. Use fewer animation frames

   Raising the playback speed keeps the motion convincing with fewer frames. Against a budget this tight, this is the biggest lever.

4. Lower the effect intensity

   The wider the shake or rotation, the more each frame differs from the last, and the less compression can do.

When you upload, you choose the name that goes between the colons in :name:. It cannot be changed afterwards, so it is worth deciding up front.

• Keep it short: people pick from autocomplete, and a long name gets buried before they finish typing
• Share a prefix: for a set, a prefix like team- makes the whole family appear together in autocomplete
• Avoid clashing with standard emoji: existing names are unavailable, so have a fallback name ready

PochiSta adjusts automatically at export time so the limit is not exceeded.

• Static: if it is over the limit, colors are reduced step by step until it fits
• Animated: it re-encodes by reducing colors first, then dropping frames. If it still does not fit, the export screen shows the actual size next to the limit

A bulk download puts the correctly sized files into a slack/ folder, ready to upload as they are.

• What to do when a Discord emoji exceeds 256KB
• How to make emotes that stay readable in chat