Bulk Image Compressor

How to use the bulk image compressor

1. Select your images.
2. Choose a format and quality — 80% is a good start.
3. Process, check the saving per file, then download the ZIP.

About this tool

One quality setting applied to a whole selection, with the before and after size shown for each file so you can see where the saving actually came from.

Quality around 80 per cent is a sensible default for photographs and typically removes half the total weight or more. Because the setting is shared across the batch, results vary by image: a busy photograph compresses well, while a screenshot or a graphic with sharp text will show visible artefacts at the same setting. If a batch mixes both, compress them separately rather than accepting a compromise that suits neither.

WebP usually beats JPEG at matching quality, often by a further quarter, and every current browser displays it.

The totals are worth reading rather than the percentages alone. A batch can report a large percentage saving that amounts to very little in absolute terms, or a modest one that removes tens of megabytes.

Batch size is bounded by memory rather than by any rule of ours, and the limit is less obvious than it looks. A decoded image occupies width × height × 4 bytes in memory no matter how small the file is on disk — a 3 MB phone photo at 4032×3024 becomes about 49 MB once decoded. That is why a dozen holiday photos can exhaust a tab while looking modest in a folder.

So files are processed strictly one at a time, and each is released before the next is opened. Peak memory stays near a single image rather than the whole batch, which is what makes a hundred files workable. If a very large batch does stop, splitting it in half is the fix.

Nothing is uploaded. The ZIP is assembled on your device too, so a batch of a hundred photos does not become a hundred uploads — which matters more for a batch than for a single file, since batches tend to be personal photo libraries or unreleased client work.

Common uses

• Cutting page weight across a site's images.
• Reducing a photo folder before backing it up.
• Getting a set of images under an email attachment limit.

Frequently asked questions

What quality setting should I use?

Around 80% for photographs, which usually removes half the file size or more without visible loss. Graphics and screenshots need more, or a different format.

Why did some images barely shrink?

They were probably already compressed, or they are graphics rather than photographs. Re-compressing an already-compressed JPEG costs quality without saving much.

Does compressing lose quality?

Yes, for JPEG and WebP — that is how they save space. The loss is invisible at moderate settings on photographs and obvious on sharp-edged graphics.