Prepare Images for Upload: Size, Dimensions and Format

An image can look fine on your phone and still fail an upload: its file may exceed the byte limit, its dimensions may be outside the allowed range, or its format may not be accepted. Treat these as separate requirements. The Image Compressor combines a size budget, optional maximum dimensions and a JPG output choice so you can prepare a copy without uploading the source file to a processing server.

Read the destination’s requirements first

Before changing the file, note the accepted formats, maximum file size and any minimum or maximum pixel dimensions. A required aspect ratio or crop is another constraint: fitting within maximum dimensions preserves the original ratio and does not crop the image into a new shape.

Keep the original. Start each new attempt from it rather than repeatedly compressing an already compressed copy. Repeated lossy encoding can discard more detail, and a small output cannot recover pixels removed in an earlier attempt.

Choose a size budget

Targets such as 100 KB, 200 KB and 500 KB are useful examples of size budgets, not rules for any particular application, employer or government service. Enter the budget that fits your actual destination, with some margin if its size convention is unclear.

This tool uses 1 KB = 1,024 bytes. Its example budgets therefore mean:

Target entered	Maximum bytes used by the tool
100 KB	102,400
200 KB	204,800
500 KB	512,000

A service may instead use 1,000 bytes per KB. An image that fits this tool’s 100 KB budget could then exceed that service’s 100 KB limit. Compare the actual byte count, and use a lower target when necessary. The target is an upper bound to try to satisfy, not a promise to produce an exact file size.

Prepare a copy in one workflow

1. Open the Image Compressor and select your image or batch.
2. Choose target-size mode and enter your KB budget.
3. Keep the input format if the destination accepts it, or choose JPG for compatible still-photo output. JPG replaces transparent areas with white; keep a transparency-capable format when transparency matters.
4. If required, set maximum width and height. The image fits within those limits while keeping its aspect ratio, and smaller originals are not enlarged.
5. Decide whether to allow further dimension reduction to reach the target. It is off by default. Enable it only when smaller dimensions remain suitable for your task.
6. Run compression and review each result’s file size and dimensions. Download successful outputs and address any individual failures separately.

For exact resizing or percentage-based changes, use the Image Resizer and consult the resizing guide. For other output formats, use Image Converter.

When the target cannot be met

At fixed dimensions, lowering encoding quality has a limit. The tool stops at 10% quality for formats with a quality setting. PNG does not have a JPEG-style quality control, so moving a quality setting cannot reliably make a PNG fit an arbitrary budget.

If compression fails, consider a larger budget if the destination permits it, JPG for a photograph without required transparency, or optional dimension reduction. Check minimum dimensions before choosing that last option. If the destination requires both large dimensions and a very small file, there may be no usable result from your source. The tool reports an unmet target rather than treating an oversized output as success.

Check the downloaded file before submitting

Open the output and inspect orientation, colors, edges and text at the size it will be viewed. Check the downloaded file’s bytes, dimensions and format against the destination’s requirements. Compression can blur fine print; reducing dimensions can make a document photo unreadable. Neither process improves an already blurry source.

For batches, a failed file does not mean successful files need to be processed again. Review the successful outputs and retry failed inputs with appropriate settings. Keep originals until all copies have been checked.

Processing happens locally in your browser, but uploading the finished copy to another service is a separate action. Meeting a file-size budget does not guarantee that service will accept the image or approve its contents.