How to compress images without ruining them

The short version: dimensions first, quality second

File size comes from two things: how many pixels there are, and how precisely each one is stored. Scaling a 4000-pixel photo down to 1600 removes 84% of the pixels and more than half the weight, with no visible change — because nothing ever displayed those 4000 pixels. Dropping quality from 90 to 60, on the other hand, saves comparatively little and starts to look noisy.

So the order is always dimensions first, quality second. Both controls are on the image compressor, and the size change is shown immediately.

A table you can copy

What each quality level looks like

• 90–100: indistinguishable from the original, comparatively heavy. Right for archives and further editing.
• 80–85: most people cannot tell. Size is already well down. This is the default answer.
• 70–79: side-by-side you can spot noise in skies and skin. Usually acceptable.
• 60–69: visible blocking, soft text edges.
• Below 60: thumbnails only.

When to change format instead of lowering quality

If you are compressing a PNG, the quality slider will do nothing — PNG is lossless, so there is no precision to trade away. Your options are smaller dimensions, or a different format. In practice a screenshot PNG converted to WebP shrinks by 50–70%, and photographic PNGs by more than 60%: PNG to WebP does it in one step. Likewise, if your JPG is still heavy, converting it to WebP usually removes another third.

Two details people forget

Metadata. Photos carry a timestamp, camera model and often GPS coordinates. None of it helps the page, all of it costs bytes. Re-exporting through a converter drops it.

Do not re-compress the same file repeatedly. Every JPG save loses a little more. Start from the original each time and compress once.

Try it

Open the online image compressor, drop your files in, set a max width, then move the quality slider — each result shows the before/after size and percentage.