What usually asks for 20 KB
Twenty kilobytes is the tightest limit most people meet, and it shows up in the same few places: scanned signatures and thumb impressions on online application forms, small ID or face photos for exam and registration portals, and avatar fields on older systems. These forms often give a range — “10 to 20 KB”, “between 4 and 20 KB” — and sometimes exact pixel dimensions as well. Read the instructions for both before you start.
Signature or face photo: what 20 KB buys you
Twenty kilobytes is 160,000 bits. Spread across a 12-megapixel phone photo (4032 × 3024) that is about 0.01 bits per pixel — no JPEG can show a photo at full size on that. So for a photo, the tool keeps the quality at a level where faces stay clean and reduces the pixel count until it fits. For a typical head-and-shoulders photo, expect something in the region of 400 to 700 pixels on the long side; a busy background pushes it smaller, a plain wall lets it stay larger. That is enough for a form's thumbnail, which is all most of these fields display.
A signature is the opposite case: mostly white paper with a few dark strokes. White compresses to almost nothing, so a signature on clean paper often fits under 20 KB at full size and high quality. If yours doesn't, the paper is probably grey, shadowed or textured — the tool is spending bytes on the paper, not the ink.
Preparing a signature so it fits
- Sign in dark blue or black ink on plain white paper.
- Photograph or scan it in even light, square on, with no shadow from your phone.
- Crop tightly around the signature — a small margin, not the whole page.
- If the form gives dimensions (for example a width and height in pixels), set them with the resizer first, then compress here.
When 20 KB can't be met
Sometimes the honest answer is no. If even a tiny version won't fit, the tool says so and shows the smallest attempt so you can see how far off it is. And if the photo only fits by shrinking below about 320 pixels on its long side, it warns you that it may no longer be recognisable, rather than presenting a postage stamp as a success. The fixes are the ones above — crop harder, use a plainer background — or check whether the form really means 20 KB and not 200 KB or 2 MB.
Even when it does fit, look at the verdict and the new dimensions together. “Good” means the compression is clean at that size; it doesn't mean a 450-pixel photo is as detailed as the original. For a face that will be checked by a person, make sure the eyes and outline are still clear.
Other limits
Need a different number? Use compress to any size in KB, or the pages for 50 KB and 100 KB. The result is a JPEG with no EXIF data, so it doesn't carry your location.