Slack Image Sizes — Workspace Icon, Emoji & Profile Photo

Workspace Icon

The workspace icon is the tile in the sidebar rail that people click to switch workspaces. Slack accepts GIF, PNG, JPG, JPEG, HEIC, and HEIF, and walks you through a crop step on upload — so a non-square source will not be rejected, it will just be cropped for you.

• Upload 512x512: Slack does not publish a minimum, but 512x512 is the same square it asks for on profile photos and it leaves headroom for the retina rail tile.
• Crop it yourself first: Slack’s in-app cropper works, but cropping in your editor is the only way to control what gets cut. Upload an already-square file.
• Ship the mark, not the logo: the rail tile renders at roughly the size of a favicon. A wordmark with a tagline is illegible there; an icon-only lockup is not.
• Corners get rounded: Slack draws the icon as a rounded square. Keep anything load-bearing away from the corners.
• PNG for flat marks, JPG for photos: the same rule as everywhere else. A transparent PNG composites cleanly against both the light and dark sidebar.

Custom Emoji

Slack is unusually terse about emoji specs. The help centre says only that square images under 128KB and with transparent backgrounds work best, that images can be JPG, PNG, or GIF, and that GIFs can include up to 50 frames. There is no published pixel maximum — but there is an enforced one.

• 128x128 is the target: big enough that Slack never has to upscale, small enough that a PNG stays well under the 128KB ceiling.
• 128KB is the real constraint: it bites on animated GIFs long before it bites on static PNGs. A 50-frame GIF at 128x128 will blow the budget unless you cut frames or reduce the palette.
• 50 frames, hard stop: Slack documents the limit explicitly. Trim the loop rather than dropping the frame rate to nothing.
• Transparency, always: emoji sit inline in messages and inside reaction pills, on white and on dark. A baked-in white background looks like a sticker on both.
• Oversized uploads are resized, not rejected: Slack downsizes them for you. The API surfaces the underlying limit as error_bad_wide and resized_but_still_too_large — so a 2000px source that compresses badly can still fail.
• Design for 22 pixels: the emoji renders inline at roughly text height. Fine detail, thin outlines, and any lettering disappear. One shape, one silhouette, high contrast.

Profile Photo

This is the one spec Slack states as an exact range: your profile picture should be a minimum of 512x512 pixels, but no larger than 1024x1024 pixels. Both ends are real. Undershoot and it looks soft on a retina screen; overshoot and the API returns too_large — the uploaded image had excessive dimensions.

• 512x512 minimum, 1024x1024 maximum: anywhere in that square range is fine. 1024x1024 is the safest choice if you want the crispest render on high-DPI displays.
• Square, or Slack crops it: the photo is displayed as a rounded square next to every message you post.
• JPEG, PNG, or GIF: anything else fails with bad_image.
• Animated GIFs have a frame limit too: the API rejects them with too_many_frames. A still photo is the safe path.
• Crop tight: the avatar renders at around 36 pixels in the message list. Head and shoulders, not a full-body shot.

Shared Images & File Previews

You can upload a file up to 1GB to Slack — but the image everyone actually sees is much smaller. Slack generates a fixed ladder of thumbnails for every uploaded image and renders the 360px one inline in the message. That is why your 2560px desktop screenshot arrives unreadable.

• Crop, don’t shrink: a full-screen 2560px screenshot squeezed into 360px turns 12px UI text into mush. Crop to the region you are actually talking about and it survives the downscale.
• 1024px on the longest side is enough: that is the largest thumbnail Slack generates. Uploading a 4000px original buys nothing but upload time.
• 1GB per file: the ceiling applies to anything you add to a channel or DM, not just images.
• Animated GIFs get animated thumbnails: Slack renders thumb_360_gif and thumb_480_gif so the loop plays inline rather than freezing on a still.
• Link previews come from Open Graph: when someone pastes your URL, Slack unfurls it using your page’s og:image. A 1200x630 card — the same 1.91:1 master you already ship for LinkedIn and X — covers Slack too.

Frequently Asked Questions