What the slider changes
JPEG splits the image into small 8×8 blocks and stores each one as a mix of patterns. The quality setting decides how precisely those patterns are kept: lower quality rounds them more coarsely, which saves space but creates blocky artefacts and halos around sharp edges.
Typical results
| Quality | What you see | Use for |
|---|---|---|
| 90–100% | Indistinguishable from the original; much bigger files | Archiving, printing, further editing |
| 75–85% | Hard to tell apart at normal viewing; files several times smaller | Websites, shops, social media, email |
| 50–70% | Slight softness and artefacts on close inspection | Thumbnails, strict size limits |
| below 50% | Visible blocks and colour bands | Avoid |
Common myths
- “100% is lossless.” No — JPEG at 100% still compresses with small losses. For lossless use PNG.
- “The percentage is the same in every program.” No — each encoder maps quality differently, so 80% in one app may differ from 80% in another.
- “Saving again does no harm.” Each re-save at lossy quality loses a bit more. Edit from the original and export once.
Find the sweet spot quickly
In Compress image move the quality slider and compare file sizes in the list; or switch to “Target size” and let the tool find the highest quality under your KB limit. For very large photos, reduce the dimensions first — see how to reduce an image to 100 KB.
Frequently asked questions
What quality should I use for Instagram?
Upload a high-quality JPG (about 85–92%) at 1080 px wide; Instagram recompresses every upload anyway.