Compress a JPEG to an Exact KB Size

Hitting an exact file size is a search problem, because JPEG encoders accept a quality number, not a byte count, and the relationship between the two depends entirely on image content. This tool runs a binary search across the quality range 20 to 95: encode at the midpoint, measure the bytes, then narrow the interval up or down. After about seven passes it converges on the highest quality that still fits under your number.

Sometimes even quality 20 overshoots the target. That happens when there are simply too many pixels for the byte budget - a 4000-pixel-wide portrait cannot become 20 KB at any quality worth looking at. When the search bottoms out, the tool enters downscale rounds: dimensions shrink by a factor of 0.9 and the quality search repeats, looping until the target is met. You end up with the largest dimensions and best quality the byte limit physically allows.

Application portals are the main reason this page exists. Recruitment sites commonly demand a photo between 20 and 50 KB and a signature between 10 and 20 KB, and they reject anything outside the window - sometimes including files whose pixel dimensions are wrong. Read your portal instructions for both constraints, set the pixel size first if one is specified, then let the KB search handle the rest.

One caution about aiming absurdly low: ID cards and documents lose legibility faster than faces do, because compression attacks exactly the sharp strokes that letters are made of. If a form accepts a range, target the top of it rather than the bottom - a 48 KB photo under a 50 KB cap looks dramatically better than a 21 KB one and passes the same check.