Compress image for Slack Attachment
Slack's free tier accepts uploads up to ~ 1 GB but every extra MB slows the workspace search index.
Your images stay on your device. Nothing is uploaded.
Slack accepts attachments up to ~ 1 GB per file but every uploaded image consumes workspace storage and slows the search index. Sending a 1 MB photo instead of a 15 MB camera raw is one of the more considerate optimisations you can do for your team.
This preset produces a 2048 px JPEG at quality 88 — high-quality but Slack-storage-friendly.
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Frequently asked questions
- What size should an image be for Slack message attachment?
- The preset on this page reflects the recommended dimensions for Slack message attachment. Uploading at these dimensions avoids the auto-crop or auto-downscale that the platform would otherwise apply.
- Does the platform re-encode after upload?
- Yes — most platforms re-encode uploaded images to their internal format and bitrate. Starting from a clean, correctly sized image means only one round of lossy re-encoding rather than two.
- What format should I use for Slack message attachment?
- The preset uses the format recommended for Slack message attachment. JPEG is the safest universal choice; some workflows benefit from WebP or PNG for specific reasons (transparency, screenshots, etc.).
- Is anything uploaded?
- No. The compression and resize run in your browser. The image only leaves your device when you upload it to Slack message attachment yourself.
- Can I batch process multiple images for Slack message attachment?
- Yes — use the bulk compressor to process a folder of images with the same settings. Every image gets the correct dimensions and quality for Slack message attachment.
Prepare a Slack — message attachment image.
Drop your image — the tool applies the correct dimensions and quality for the platform.
Start compressing