When bulk resizing is the right tool
Any time the same transformation applies to many files: preparing a product catalogue for a store, shrinking a holiday album before emailing it, generating web-ready versions of a photoshoot, or converting a directory of PNGs to WebP for a site build.
Because the work happens locally, the time it takes scales with your CPU rather than with your upload speed — which is usually the slower of the two by a wide margin.
Choosing settings for a batch
One set of settings covers every file, so pick for the batch rather than for any single image. A few rules that hold up well:
- Set the width and leave the height to follow the aspect ratio. A fixed width with a fixed height will distort any image whose proportions differ from the target.
- For web use, 1200–1920px wide covers nearly every layout, and WebP at quality 80–85 is visually indistinguishable from the original at a fraction of the size.
- For email, cap the longest edge around 1200px and use JPEG at quality 80 — recipients care more about the attachment opening than about pixel-level fidelity.
- Keep your originals. Bulk operations are lossy and there is no undo once the ZIP is the only copy you have.
Working with large batches
Each image is fully decoded into memory before it is resized, so a batch of very large photos can exhaust a tab’s memory budget on a phone or a low-RAM laptop. If processing stalls or the tab reloads, split the batch into smaller groups.
Millimetre dimensions here are converted at 300 DPI, the standard print resolution — so a 35 × 45mm setting produces 413 × 531 pixels.
Frequently asked questions
- How many images can I resize at once?
- There is no fixed cap — the practical limit is your device's memory, since every file is decoded in the browser. A few hundred photos is usually fine on a desktop; on a phone, work in smaller batches.
- Are the files uploaded anywhere?
- No. Each image is decoded, resized and re-encoded in your browser, then added to a ZIP that is also built locally. Nothing is transmitted.
- What is the file size limit per image?
- 10MB per file for bulk processing. The single-image resizer accepts up to 25MB.
- Can I apply different sizes to different images?
- Not in one pass — bulk resizing applies one set of settings to every file, which is the point of it. Run separate batches for separate sizes.