Reduce image size in KB, not just "make it smaller"
Upload forms state a limit, such as "JPG, maximum 50 KB", and reject anything above it. This image size reducer starts from that number. You type the KB limit, and the page searches for the best-looking version of your image that is at or just under it, then shows the exact size before you download.
How the image size reducer works
- Quality first. The image is saved as a JPG at a high quality. If that is too large, the page tries lower qualities, halving the gap each time, until it finds the highest quality that fits your limit.
- Pixels only when needed. If even 30% quality is still over the limit, the width and height are reduced in small steps until the image fits at a reasonable quality, and then the quality is raised again as far as the limit allows.
- A clean copy. The result is a new image, so camera details and location data stored by phones are left out. Your original file is not changed.
That order matters. A photo at a slightly lower JPG quality usually looks better than the same photo at half the width, so the pixel size is the last thing to change.
Compress image in KB for a specific size
Any number works, from 5 KB to several MB. For the sizes asked for most often there are pages with advice for that size:
- Compress image to 20 KB: signatures, thumb impressions and small photos.
- Compress image to 50 KB: passport-style photographs for application forms.
- Compress image to 100 KB: clearer photos and single-page document scans.
- Compress image to 200 KB: certificates, full photos and larger scans.
Resize image in KB and in pixels together
Some forms set two limits, for example a photo of 200 x 230 pixels under 50 KB. Open Width and height, type the pixels, and choose Exactly this size to fill those dimensions (the edges are trimmed evenly if the shape differs) or Fit inside to keep the whole picture. The KB limit then applies at that size. If the size is set in cm, the image resizer in cm converts it to pixels at the DPI you choose.
When the file is too small instead
Some forms also reject files below a minimum. If a signature comes out smaller than that, use increase image size in KB, which raises the quality and, if needed, the pixel size, without stuffing the file with empty data.
What happens to your image
The whole job runs in your browser, in a background worker where the browser supports one. The image is never uploaded, so this is also fine for ID documents and photos you would rather not send to a website. See all image tools, or how the page can be checked in your browser's developer tools.
The image is redrawn with your browser's own canvas, so the result depends on the browser's JPG, PNG and WebP encoders. MDN's image file type guide explains which format suits photos, signatures and scans.