How to compress an image to an exact size in KB

The quick way

1. Open Compress to Size and drop your image.
2. Type the limit in KB, or pick a common one such as 20 KB, 50 KB, 100 KB or 1 MB.
3. Keep Save as JPG for photos unless the form asks for another format.
4. Compress, then check the reported size, quality and dimensions before you upload.

How it finds the right setting

An encoder cannot be told to produce a file of a given size. It can only be given a quality setting, and the resulting size depends on the picture: a detailed landscape needs more bytes than a plain portrait at the same quality. So the tool searches. It encodes at one quality, measures the result, then narrows the range up or down until it finds the highest quality that fits under your target.

If even a very low quality is still too big, it reduces the pixel dimensions step by step until the file fits. If you turn off Shrink dimensions if needed, the size in pixels is kept and you get the smallest file it could make, which may be above your target.

Why the result is just under the target

Because quality moves in steps, the result lands at or a little below the limit rather than on the exact byte. That is what upload forms want, since the limit is a maximum.

KB can mean 1,000 or 1,024 bytes. This tool counts 1 KB as 1,024 bytes, and so does Windows, while macOS counts 1,000. If a form counts 1,000 bytes and rejects a file that looked fine, set a target a few KB lower.

Forms with a minimum size or exact dimensions

Some portals reject files that are too small, for example a photo that must be between 20 KB and 50 KB. Set a Minimum size under More options and a JPG that comes out smaller is padded with filler data to reach it, without changing how it looks.

Passport, visa and exam portals often fix the pixel size as well. Passport & Form Photo combines the exact dimensions with the KB limit for common specifications. Requirements change, so check the official rules of the portal you are using.

Getting the best quality under a small limit

• Crop away what the form does not need. Fewer pixels leave more bytes for the face or document that matters.
• Very small limits such as 10 or 20 KB suit small images a few hundred pixels across. A large image squeezed under a tiny limit will look soft.
• Plain backgrounds compress far better than busy ones.
• If the form accepts it, WebP or AVIF fit more quality into the same size, but many forms only accept JPG.

Limitations

Scans and screenshots of text lose legibility quickly at small sizes. If a document becomes hard to read, raise the limit if the form allows it, or crop to the essential part. Because the tool runs in your browser, ID documents and passport photos are never uploaded while you compress them.