Most image compressors give you a quality slider and wish you luck. You pick 80%, export, check the size, and repeat until the file fits under the limit. ToolsByUs Compress Image does it the other way round: you state the target size, and the tool finds the settings that land on it.

The whole thing runs in the browser. The file's contents never leave the tab — there is no upload step at all.

The worked example

I took a 4032x3024 JPEG photo and asked the tool for exactly 200 KB:

  • Original: 415 KB (424,449 bytes)
  • Target: 200 KB
  • Result: 193 KB — 46% of the original, a 54% reduction
  • What changed: the dimensions stayed at 4032x3024, the format stayed JPG, and no max-width resize was applied. In Target size mode, with "Under 200 KB" and Format set to "Same", the tool binary-searched the quality to land under the target, finishing in 1.3s.

The preview the tool shows is the real encoded result, not a simulation — what you see is the file you download.

Why "exact target" is a different problem from "quality 80%"

A quality slider controls one variable; file size is the outcome of quality, dimensions, format, and image content together. Hitting an exact size means searching that space: try settings, encode, measure, adjust, encode again. Doing that search locally, in the browser, is the interesting engineering part — every encode is real work on your machine, and the tool has to converge without making you wait through dozens of visible attempts.

That is also why the preview matters. If the tool only estimated the size, you would still be guessing. Showing the actual encoded output means the number on screen and the file you download agree.

The numbers that surprised me

  • ToolsByUs ships 135 free tools, all client-side, in 6 languages — the compressor is one tool in a suite built on the same idea: the file never leaves the browser.
  • The compressor handles JPG, PNG, and WebP, by quality or by exact target size.

Honest caveats

  • Exact-target compression is a trade-off, not magic. A photo with fine detail (foliage, crowds) will lose visible quality faster than a flat graphic when squeezed to the same size. If the result looks bad, the honest fix is a bigger target or smaller dimensions, not another pass at the same size.
  • Everything runs in the browser tab, so a very large image depends on your device's memory and CPU. That is the price of never uploading: your machine does the work a server would have done.
  • "Your file's contents never leave the browser" is a narrower claim than "fully anonymous" — the site's analytics is configured separately. Keep the two apart.

If you have ever re-exported the same image four times to get under an upload limit, stating the target size up front is the saner workflow. One tool that does it, free, with no upload: https://toolsbyus.com