How to compress an image to a target size (100KB, 200KB, 500KB)
A registration system that wants "a photo under 100KB," an email attachment limit, a forum avatar cap — these all need an image squeezed to a specific size. This explains how to do it, and why sometimes no amount of compression reaches the target.
Use Target size mode
In the image compressor, choose Target size and enter the KB you need (say 100). The tool repeatedly adjusts the encoding quality — keeping the pixel dimensions fixed — to approach that size. That is far easier than guessing quality values by hand.
Mind the unit: 1KB here is 1024 bytes, matching most systems. If the requirement is "under 100KB," setting the target around 95 is safer, leaving a little margin.
If it will not shrink, the dimensions are too big
When the file is still over target at the lowest quality, the problem is usually not quality but pixel dimensions. A 4000×3000 photo cannot easily drop under 100KB no matter how low you push quality, because the pixel count alone is too high — and the picture would look terrible.
The right order is: resize the width and height down first (long edge to 1000–1500px, say), then compress. With fewer pixels the size falls sharply at the same quality, and the result is cleaner. For ID photos and avatars, around 1000px is plenty.
Format affects the result too
WebP usually gives the smallest file at a given quality, so prefer it when the target platform supports WebP. If the platform only accepts JPG — many old systems do — choose JPG. Avoid compressing icons or text screenshots to JPG just to save size; they show obvious noise at low quality. Keep such content at higher quality, or resize it first.
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