What Slack asks for, in one table. Pick a row to resize your image for it, right in your browser.
| Tool | Output | Sizes (px) | Formats | Max file size |
|---|---|---|---|---|
| Slack Emoji Resizer | Slack emoji | 128×128* | PNG, GIF | PNG 128 KB, GIF 128 KB |
* Our pick: no exact size is published for this, so we export one that stays sharp.
Checked against Slack's help pages. Oldest check: 2026-10-24.
Slack publishes a few simple rules for custom emoji: JPG, PNG or GIF, square images under 128KB with transparent backgrounds work best, and GIFs can have up to 50 frames. The table above shows what ImgWrench exports, and the row links to a free tool that makes it.
Open the Slack emoji resizer from the table above and drop in your image or GIF. It makes a square 128×128 emoji, keeps GIFs to 50 frames and shrinks anything over 128KB, then you download one file or a ZIP and add it in Slack. It all happens in your browser, so nothing is uploaded.
Slack recommends square JPG, PNG or GIF images under 128KB with transparent backgrounds, and allows GIFs of up to 50 frames, without giving a pixel size. The Slack emoji resizer exports 128×128, our own pick.
Slack publishes no pixel size, only that square images under 128KB work best. Rather than invent an official number, ImgWrench uses 128×128, a size we chose because it's sharp at the small size emoji appear at and leaves room under 128KB. It's also the size Discord recommends for its emoji, so one file works on both.
Yes. In the Slack emoji tool, tick Discord emoji to get a matching 128×128 Discord copy, checked against Discord's 256KB limit, from the same crop. Twitch emote sizes are there too. For Discord stickers or banners, open the Discord image sizes page.
No. Every ImgWrench tool runs entirely in your browser, so your images are resized on your own device and never sent to a server. Nothing is stored or shared. You can check this yourself: open your browser's network tab while you resize and download, and you'll see no image data leave the page.