Slack emoji size and requirements

Slack custom emoji requirements at a glance

Slack is strict about the file you upload as a custom emoji. These are the values to hit, and the ones this tool targets automatically:

• Dimensions: 128 × 128 pixels (square).
• File size: 128 KB or less.
• File types: PNG, JPG or GIF. Animated GIFs are supported.
• Name: lowercase, no spaces; use letters, numbers, dashes or underscores.
• Animation: this tool keeps animated GIFs animated and reduces them to at most 50 frames if needed to fit 128 KB.

Why 128 × 128 pixels?

Slack displays custom emojis small, inline with text and in reactions, so 128 × 128 is plenty and keeps files light. Extra resolution adds nothing visible, only weight, which is why a simple crop and resize fixes most upload errors.

How to get a Slack emoji to the right size

Your image is probably not square, or it is much larger than 128 × 128. Choose the part of the picture you want with the square crop above, and the tool resizes it to exactly 128 × 128 px. Static images are saved as a PNG (transparency is kept); animated GIFs stay animated GIFs.

If the result is still heavier than 128 KB, the tool reduces the number of colours, and for animations the number of frames, until it fits. The result screen tells you the final file size.

Everything happens in your browser: your image is never uploaded. If your file is too heavy, see why your Slack emoji is too big. To add the result to your workspace, follow how to add a custom emoji to Slack.

Frequently asked questions

What is the exact size of a Slack emoji?

A Slack custom emoji is 128 × 128 pixels and must be 128 KB or smaller.

Can a Slack emoji be bigger than 128 × 128?

Slack expects 128 × 128 pixels, and emojis are displayed small, so extra resolution only adds weight. Upload a 128 × 128 file under 128 KB to avoid errors.

Does the emoji have to be square?

Yes, aim for a square. Emojis are shown in a square, so a non-square image can look distorted or cut off. Crop it to a square first.