Compress Images to 20KB

20KB is one of the smallest limits in real use

Twenty kilobytes is a fraction of what a photograph naturally needs, and it is specified by real systems rather than invented: government passport application forms, examination submission portals, and some job application forms set limits in that range. A modern phone photo is typically two to four megabytes, so reaching 20KB means removing more than 99 percent of the file. That is only achievable with a combination of reduced dimensions and efficient encoding, and it is why the honest answer at this size is usually that the image must also be smaller.

NoteA form asking for 20KB is normally expecting a small image too. Check what dimensions it specifies.

The two things a passport or exam form usually also specifies

A file size limit on a passport or examination form almost never comes alone. The same instruction normally also gives required pixel dimensions, and often a maximum for height and width separately. A 35 by 45 millimetre photo at 300 DPI is 413 by 531 pixels, which is a completely different request from an arbitrary 20KB. Following the stated dimensions and then compressing to the limit is the correct order, and following the file size alone is what produces the soft, enlarged result people complain about.

• Read the whole instruction, not just the file size.
• A stated millimetre size converts to pixels at 300 DPI.
• 35 by 45 mm at 300 DPI is 413 by 531 pixels.
• Resize to the stated dimensions first, then compress to the limit.
• Some forms specify a maximum width and height instead of an exact size.

NoteResizing to the stated dimensions first is what makes the result sharp rather than soft.

Format, and why it matters more at this size

At 20KB the format is not a detail, it is most of the strategy. JPG discards detail to reach a small size and produces banding at very low quality. WebP is substantially more efficient, so it holds a cleaner image at the same byte count, and AVIF is better again. A flat background, which is what a passport photo has, compresses extremely well in any of them. If the form insists on JPG, expect a softer result than the byte target would otherwise allow, and check the output visually rather than assuming the number is the whole story.

• WebP holds a cleaner image at 20KB than JPG does.
• AVIF is better still where the form will accept it.
• A plain background, typical of a passport photo, compresses very well.
• If the form requires JPG, expect a softer result at this size.

Meeting the limit honestly

A file already under 20KB is passed through unchanged rather than degraded for no benefit, and a target that cannot be met at an acceptable quality is reported rather than disguised as a success. The reliable route at this size is to reduce the dimensions, and the tool reports the byte count so it can be checked against the form before submitting. A file that the tool reported as within the limit and the portal still rejected usually means the portal applies a stricter rule, in which case going smaller is the answer.

• Already within the limit: the file is copied through unchanged.
• An unreachable target is reported honestly, not disguised.
• Reducing the dimensions is the reliable way to reach 20KB.
• Check the reported byte count before submitting to the form.
• If a portal rejects a compliant file, it applies a stricter rule. Go smaller.

NoteA file reported as within the limit and still rejected means the portal counts differently. Go smaller.