Compress an Image to 20 KB

Twenty kilobytes is 163,840 bits. Divide that by the number of pixels and you get the average number of bits the encoder can spend on each pixel:

The fewer bits each pixel gets, the more blocky and smeared a JPG looks. That is why a signature fits easily, a passport-size photo usually fits with acceptable quality, and a full phone photo has to be shrunk heavily.

The tool first draws your image at full size (anything longer than 4096 pixels on its long side is reduced to 4096 px) and encodes it at quality 0.8. If that file is already at or under the target (and not larger than your original), you get it straight away. If not, it repeats up to 10 times. On each pass it multiplies the quality by 0.95 (0.85 for PNG) and, because the first attempt was too big, also shrinks the width and height to 95% of the previous pass.

Ten passes is the limit. After all ten, the width and height have dropped to about 60% of where they started and the quality setting to about 0.48. If the file is still too big at that point, you get the last attempt and a note saying the target was not reached.

• Crop tightly. White margins around a signature still cost bytes. Use the Crop tool first.
• Use the dimensions the form asks for. Many forms specify both size and pixels (for example a fixed width and height). Set those with the Image Resizer, then compress here.
• Pick JPG if the form says JPG. WebP fits more detail in 20 KB, but a form that only accepts JPG will reject it.
• Scan or photograph on plain white. Paper texture and shadows are detail the encoder has to store.

Large photos can still be above 20 KB after ten attempts. The tool tells you when that happens. Resize to a few hundred pixels wide and run it again; at that size 20 KB is usually enough. If you need a bit more room, the 50 KB page uses the same method with a larger budget.

Compression runs in your browser. Signatures and ID photos are not uploaded to Image York.