Compress Image to a Size

Upload forms give you a number. "Photograph must be under 100 KB." Every compressor gives you a quality slider, which is a different question — so you set it to 60, check, set it to 40, check again, and repeat until something fits.

This does that loop for you. It encodes at high quality first, measures, and narrows in by halving the range each time. If quality alone cannot reach your figure it reduces the dimensions and searches again — because past a point, fewer pixels at decent quality look better than the same pixels at bad quality.

It aims to land just under. If the form allows 100 KB and the search finds a version at 97 KB, that is the answer. Coming back with 30 KB would mean having thrown away three quarters of the detail the form was willing to accept.

Why this is rare. Hitting a specific size means encoding the image ten or more times. That is processing a server pays for on every visit, which is why free tools hand you a slider instead. The work here happens in your browser, on your own processor, so the expensive approach is the one that costs nothing.

The number is decimal. 100 KB means 100,000 bytes, because that is what the form checking your upload almost certainly means. Being cleverer than the form is how you fail the form.

WebP reaches a given size at noticeably better quality than JPEG and is accepted almost everywhere now. If the form insists on a JPEG, use JPEG — but if it does not, WebP will look better at the same limit.

A visa application wants a passport photograph under 100 KB, in JPEG. The picture from your phone is 4.2 MB.

Choose it, press 100 KB, press fit. It tries quality 95 — far too big — then quality 30, still too big at this resolution, so it reduces the dimensions and searches quality again at the smaller size. Four more attempts and it settles at 96 KB, 900 pixels tall, quality 78.

The panel shows the original and the result side by side with a wiper, so you can check the face before submitting rather than after being rejected.

If you had asked for 20 KB instead, it would have told you that the smallest it reaches is 34 KB and that going further leaves an image not worth having. That is a more useful answer than a file that meets the number and gets your application returned.