Calculator
What the Bulk Image Resizer does
Bulk Image Resizer: resizes every selected image locally in your browser, one file at a time, and gives each result its own preview and Download button. Everything runs in your browser and the file is never uploaded.
Pick a file and the Bulk Image Resizer processes it right here in the page. Processing is local, so speed depends on your machine rather than someone else’s server load.
It is mostly used by writers preparing assets for a post. Getting the dimensions right before upload avoids a lot of downstream cropping.
Nothing is transmitted: the file is decoded and re-encoded entirely in the browser.
Field definitions, the method, and a worked example from the default values are all set out further down the page.
What do the Bulk Image Resizer fields mean?
The Bulk Image Resizer uses 4 inputs. Rather than an empty form you get a filled one, useful when you only want to test a single change.
| Field | What to enter | Default |
|---|---|---|
| Image files | stays on your device | none |
| Target size | choose from 64px, 128px, 256px, 512px, 1024px or 1536px | 512px |
| Output format | choose from PNG, JPEG or WebP | PNG |
| Quality % | accepts 10 to 100 | 90 |
How does the Bulk Image Resizer work?
Each output is derived from the inputs above in a single pass; there is no hidden state carried between runs, so the same inputs always give the same result.
Inputs are validated before anything is computed, so a bad entry is reported rather than quietly producing a wrong answer.
What a typical run looks like
You provide: Image files, Target size, Output format and Quality %
What happens: the file is read into memory by your browser, processed locally, and offered back as a download. It is never uploaded.
You get back: the finished file to download, with a line in the panel saying what was done.
Because the work is local, speed depends on your device rather than our servers, and large files are limited only by available memory.
Batch resizing sizes
Batch resizing runs the same pipeline over many files at once, sequentially, so the tab stays responsive between images. The tool processes up to 60 files per run. Select more and it resizes the first 60, tells you how many are left, and you run the remainder as a second batch.
| Use | Value | Ratio |
|---|---|---|
| One run | up to 60 images | processed in one go |
| Larger batch | over 60 images | run again for the remainder. Nothing is lost, just queued for the next pass |
| Per-image cost | ~48 MB decoded for a 12MP photo | why very large batches are chunked rather than unbounded |
Worth knowing
- Each image is decoded to raw pixels in memory before resizing. A 12-megapixel photo occupies roughly 48 MB decoded, regardless of its file size on disk, which is why processing is capped and sequential rather than all-at-once.
- If you have more than 60 images, run the tool again on the rest. Each run is independent and just as fast.
- Mixed aspect ratios in one batch will produce inconsistent results unless you resize by a single dimension rather than to fixed dimensions.
- Nothing is uploaded, so a batch of confidential images never leaves your device.
Platforms revise their published specifications from time to time. Where a ratio and a pixel size conflict, match the ratio — every platform downscales an oversized image, but none of them will fix a wrong shape except by cropping it.
How to use it
- Choose your file under Image files, or drag it onto the drop area.
- Pick a value for Target size: the options are 64px, 128px, 256px, 512px, 1024px or 1536px.
- Pick a value for Output format: the options are PNG, JPEG or WebP.
- Put Quality % (10 to 100).
- Press Resize All.
- Look at Status in the output panel.
- If you need a record, Copy Link saves the inputs and Print produces a clean page.
What this tool does not do
- Re-encoding a lossy format such as JPEG always loses some detail, even at maximum quality.
- EXIF metadata may be dropped during processing, which is usually desirable but is worth knowing.
- The tool answers exactly the question it is given; it cannot know the context around your numbers.
- Garbage in, garbage out: confirm each figure means what you think it does before trusting the result.
- Because everything runs locally, processing speed depends on your device rather than our servers.
Frequently asked questions
4 things: Image files, Target size, Output format and Quality %. A starting value is in place for each, so the form is usable immediately, without filling anything in first.
Quality % accepts 10 to 100. Anything beyond those bounds is flagged rather than approximated.
No. The file is read by your browser and processed inside the page. It is never sent to us, which is also why it keeps working offline once loaded.
No cost and no account. Use it as often as you like.
It is exact within the stated method. Anything the method does not model is simply out of scope.