Pick any JPG tool and you will see a quality slider that goes from 0 to 100. Most people assume "100" is the original, untouched, and that anything less is a percentage of perfection. That is not how JPG works.
What "quality" really means
JPG quality is a knob that controls how aggressively the encoder discards information your eye is unlikely to notice. At 100, the encoder discards almost nothing — but the file is still encoded, so even "100" is not pixel-identical to the original. At 1, the encoder throws away almost everything that is not strictly required to draw a rectangle.
The relationship between the number and the file size is non-linear. Going from 100 to 90 might cut the file in half. Going from 50 to 40 might only save a few percent. The biggest savings live in the high range.
What each level actually looks like
| Quality | Typical file size vs source | Visible artifacts |
|---|---|---|
| 100 | 70–90% of PNG source | None to the eye |
| 95 | 40–60% | None to the eye |
| 90 | 25–35% | Imperceptible at normal viewing distance |
| 85 | 15–25% | Imperceptible on photos, very slight on flat areas |
| 80 | 10–18% | Very slight blockiness on close inspection |
| 75 | 8–14% | Slight softening in fine detail |
| 70 | 6–10% | Visible banding in skies and gradients |
| 60 | 4–7% | Clear blockiness and colour shifts |
| 50 and below | 2–5% | Obvious artifacts, ugly text |
Best defaults
Quality 82 is the sweet spot for almost everything: small enough to ship to the web, large enough that no normal viewer will notice anything wrong. That is the value Photoshop, Affinity Photo, and most CDN image components default to.
When to go higher
- Archive masters you intend to re-edit.
- Photography portfolios where you control the entire pipeline.
- Print-ready exports where every detail counts.
When to go lower
- Thumbnails — nobody sees them at full size.
- Background images that will be blurred or overlaid with text.
- Hard form size limits like 100 KB.
Frequently asked questions
Is JPG 100 the same as the original?+
No. Even at 100, JPG re-encodes the image. The result is visually indistinguishable but not pixel-identical to a PNG source.
Why does saving twice at quality 90 look worse?+
Each save throws away a little more detail. The errors stack on top of each other. Always work from the original master.
Do all encoders interpret the quality slider the same way?+
No. Quality 80 in one encoder might look closer to 75 in another. Trust your eyes, not the number.