Why is my Slack emoji too big, and how to fix it

Slack rejects custom emojis heavier than 128 KB or that are not 128 × 128 pixels. The fix is almost always the same: crop to a square, resize, and reduce the file weight.

Open the converter

Step by step

  1. Check the dimensions

    A 2000-pixel photo is far over the limit. Crop it to a square and scale it to 128 × 128 pixels.

  2. Check the file size

    The file must be 128 KB or less. Fewer colours and, for GIFs, fewer frames reduce it.

  3. Convert with the tool

    Drop the image in the Slack Emoji Converter: it crops, resizes and compresses automatically and shows the final size.

The usual causes

  • The image is much larger than 128 × 128 pixels (photos, screenshots).
  • The image is not square, so it needs cropping.
  • A PNG with many colours or gradients is heavier than expected.
  • An animated GIF has too many frames, colours or too long a duration.

How to fix it

Crop to a square, downscale to 128 × 128, and compress. The converter does these three steps in your browser and keeps transparency. For static images it saves a palette PNG (up to 256 colours), which is typically much smaller than a truecolour PNG.

For animations, the tool reduces colours first, then frames, then size. If a GIF still does not fit, trim it to a shorter loop first. See how to make an animated Slack emoji.

When it is still too big

Very detailed or long animations may not reach 128 KB without looking bad. Simplify the artwork, crop tighter, or shorten the loop. All the limits are listed in Slack emoji size and requirements.

Frequently asked questions

What is the maximum file size for a Slack emoji?
128 KB. The image must also be 128 × 128 pixels.
Why does my small-looking image exceed 128 KB?
File size depends on colours and detail, not only on pixels. Gradients, photos and long GIFs are heavy even when small.

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