Compress an image to 20 KB

Where 20 KB limits come from

Signature uploads, mostly. Indian bank and public-sector recruitment notices tend to follow one template, for example the Reserve Bank of India's:

The signature has to be in black ink on white paper, and signatures in capital letters are refused. Other organizations change the numbers, so the notice you are applying under always wins. Note that both rows have a minimum as well as a maximum; see below for what to do when a file comes out too small.

What fits in 20 KB

In our tests, at decent JPEG quality:

So 20 KB is roomy for a signature and tight for a photo. If a form wants a photo under 20 KB, it almost always gives a small pixel size too. Enter that width as the max width: fewer pixels leave more of the 20 KB for quality.

Scanning a signature that compresses well

• Sign larger than you need with a black pen on plain white paper, then crop tightly around the signature. Empty paper is wasted bytes.
• Use even light. Shadows and grey-looking paper turn into texture, and texture is what makes JPEG files big. Daylight from a window works well.
• Use your phone's document scan mode if it has one (the Notes app on iPhone, Google Drive on Android). It whitens the paper and straightens the page.
• Crop before compressing. The crop tool cuts the signature out at any shape; bring the result back here.

When the form says the file is too small

The template above wants a signature of at least 10 KB, and a clean 140 × 60 px signature is only about 4 KB even at top quality. Enter 10 under Minimum size: the tool first raises the quality, and if the file is still too small it adds invisible padding (a JPEG comment) until it reaches 10,240 bytes, which passes whether the form counts 1 KB as 1,000 or 1,024 bytes. The signature itself isn't changed. A larger scan, such as 300 × 120 px, also works, but in these notices the pixel size is labelled "preferred" while the file size range is a requirement.

20 KB, KiB, and the 20,000-byte target

The target is 20,000 bytes. A form that counts 1 KB as 1,024 bytes allows 20,480, so the file passes either way. Windows shows it as 19 KB and a Mac as 20 KB. The full story is on the 50 KB page.

How to compress to 20 KB

1. Drop the photo or signature here, or several at once.
2. 20 KB is already selected. If the form gives a pixel width, enter it as the max width.
3. Check the size and dimensions shown for each file. Keep JPG: it's the format these forms ask for.
4. Download.

For the photo half of the same form, switch to the 50 KB target. All the processing happens in your browser.