Compression is only half the problem
Most oversized web images are not under-compressed — they are the wrong dimensions. A 4000-pixel-wide photo displayed in a 600-pixel column wastes roughly 97% of the pixels it downloads, and no quality setting fixes that. Because file size scales with area, halving the width cuts the file to about a quarter.
So the order that actually works is: resize first, then compress, then pick a modern format. If you are not sure which images on your site are oversized, scan the page — it reports every image's natural size against the size it actually renders at.
Choosing a quality setting
| Quality | Use for | Visible loss? |
|---|---|---|
| 85–90 | Product photography, fine detail | None |
| 75–85 | Most web content (recommended) | Effectively none |
| 65–75 | Heroes, backgrounds, decorative | Rarely noticed |
| Below 65 | Only when size dominates everything | Yes — visible artifacts |
Frequently Asked Questions
How do I compress an image without losing quality?
Strictly speaking you cannot — lossy compression always discards some data. But at quality 75–85 the loss is invisible on almost all photographic content while the file shrinks dramatically. If you genuinely need zero loss, convert to WebP in lossless mode or keep PNG; you will save far less. The practical answer for the web is quality 75–85, which is what this tool defaults to.
What quality setting should I use?
Start at 75. For hero images and backgrounds you can go to 65 without most people noticing. For product photography or anything with fine detail, stay at 85. Above 90 the file size climbs steeply for almost no visible gain, which is why most images on the web are needlessly large.
Why did compressing my PNG barely help?
PNG is a lossless format, so the quality slider does not apply to it — re-encoding a PNG as PNG mostly rewrites the same pixel data. To meaningfully shrink a PNG, switch the output to WebP. It preserves transparency like PNG but compresses far more aggressively, typically 25–80% smaller depending on content.
Are my images uploaded to a server?
No. Decoding and re-encoding run entirely in a Web Worker on your device using WebAssembly builds of the standard image libraries. Your files never leave your browser, which matters for anything private, client-owned or unreleased. You can verify by watching the Network tab while compressing.
How small should my web images be?
As a rule of thumb: under 200 KB for in-article images, under 500 KB for a hero, and under 50 KB for thumbnails. If a single image exceeds 500 KB it is usually oversized in pixel dimensions rather than under-compressed — resizing it first will save more than any quality setting.
Checking images at scale?
Bulk-audit hundreds of URLs at once or hit a dimensions API from your own code.
Related tools
- PNG to WebP — usually the biggest single saving for PNGs.
- PNG to JPG — for photographs saved in the wrong format.
- Image optimization checklist.