How to use it
- Add your JPGs.
- Move the quality slider and watch the sizes update. Add a maximum size if the photos are very large.
- Download.
What the quality number really controls
JPEG splits a picture into 8 × 8 pixel blocks and describes each block as a mix of simple wave patterns, from smooth gradients to fine stripes. The quality setting decides how precisely those patterns are recorded. At high settings, even faint fine detail is kept. At lower settings, the fine patterns are rounded off or dropped, which is where the saving comes from, and eventually the block edges start to show.
Because of this, the right number depends on the photo. A picture of a clear sky compresses beautifully even at 60. A photo of gravel, leaves or a patterned shirt has far more fine detail, needs a higher setting to look good, and will always be larger. The longer explanation is in what the JPEG quality slider actually changes.
Avoid compressing the same file repeatedly
Every time a JPG is decoded and saved again, it loses a little more. Once is fine. Five or six rounds, as happens when an image is edited and re-saved or passed through several apps, and the damage becomes visible as smeared colour and blocky edges. Compress from the best copy you have, and keep that original.
Questions people ask
What is a good JPEG quality for the web?
Between 70 and 82 for most photos. Sites with large hero images sometimes go to 85 for extra polish.
Why did one photo barely shrink?
It was probably already compressed at a similar or lower quality. If the new version would be larger, the original is kept.
Does this use progressive JPEG?
The browser decides the JPEG encoding details. Files are standard baseline JPEGs, which every device reads.