Compress an image to 20 KB
20 KB target and JPG output already set. Built for signature boxes, logos and black-and-white scans, and it says plainly when 20 KB can't be reached.
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The upload box reads "Signature: JPG, 20 KB max" and the photo of your signature is 2.4 MB. A ceiling that low suits a signature, a logo or a black-and-white scan, not a photograph. Apple says a 12 MP ProRAW file is about 25 MB and 10 to 12 times larger than a HEIF or JPEG, which puts an ordinary iPhone photo at 2 to 2.5 MB: 100 to 125 times the limit, so "compress it a little" is not an option.
This page runs the search for you. With JPG selected and 20,480 bytes as the ceiling, it first tries JPEG quality between 50 and 96 at the original pixel size; if quality 50 still overshoots, it starts scaling the image down in 15% steps, searching again at each size. Each result card prints the real size, in KB to a decimal, and one of two badges, target met or smallest possible, so you know before you upload.
Be realistic about what 20 KB holds. It is a budget for flat, few-color images: a black-ink signature cropped to the pen strokes, a logo, a black-and-white scanned form. A color photo has far more to store, and the badge on the card tells you whether it made it. If the field is for a photo, reread the instructions and check which field the 20 KB applies to.
How it works
Three steps, with the 20 KB ceiling already applied when the page opens.
Drop in the signature or scan
Drag the file onto the page, pick it from your device, or paste a screenshot with Ctrl+V. A phone photo of the signed page (an iPhone HEIC included), a scanner JPG or a PNG drawn on a tablet all load, and the browser decodes them right where they are.
Check JPG, leave the slider alone
The settings panel opens with JPG highlighted on the format bar and the 20,480-byte target applied. The quality slider still sits there at 82, but nothing on this page reads it: the target search feeds the encoder its own values. Switch to PNG only if the portal rejects JPG.
Click Generate, read the badge, download
Click Generate images. Each card prints old size → new size in KB with a decimal, a width × height tag (with an arrow from the original size if the image had to shrink), an EXIF stripped tag, and target met or smallest possible. Open Compare to check that thin strokes survived, then save the file, or the whole queue as one .zip.
What 20 KB can hold
JPEG spends bytes where neighboring pixels differ, and black ink on white paper barely differs. The budget is easier to read per pixel: 20,480 bytes spread over a 600 × 200 px signature crop is 0.17 bytes per pixel; over a 400 × 500 px headshot, 0.10; over a 12-megapixel photo, under 0.002. The table is what to expect, not a measurement; the badge on the card gives the verdict.
| Image | What to expect at 20 KB |
|---|---|
| Signature cropped to the ink | The case this page is built for |
| Simple logo, stamp, icon | Few colors and flat areas: likely to fit |
| Black-and-white scanned form | Depends on the area and the size of the print |
| Color headshot, tight crop | May fit, with visible loss |
| Full document page, color photo | Only through the downscale stage |
| Photo with hair, foliage or fabric | The hardest case; expect smallest possible |
How to keep a signature out of stage two
Stage one is a search on JPEG quality with the pixels frozen. The first encode goes out at quality 50; if the file clears 20,480 bytes the search moves up, halving the gap each round until it is narrower than one point, between 50 and 96. Whatever highest quality fit is what you download, at the width × height it went in with; the dimension tag on the card then shows a single size, with no arrow.
Stage two is for whatever did not fit at quality 50. Now the page trades pixels instead. Each pass multiplies width and height by 0.85, draws the smaller image with smooth interpolation onto a white canvas and runs the same 50-to-96 search on it; the first size where a quality fits wins, and the dimension tag on the card gains an arrow. Sixteen passes is the cap, which is 0.85 to the sixteenth power, or 7.4% of the starting width, and the passes stop sooner if the longer side gets down to 64 px. In a test of ours with a 12-megapixel photo (4000 × 3000) in September 2026, the 20 KB target was met at 484 × 363.
Thin pen strokes are what stage two puts at risk, which is why the next section is about keeping the search in stage one. And if every pass misses, the page makes one last try at the smallest size, with qualities between 5 and 50; if that misses too, it does not pretend: you get the smallest file it reached, its size printed on the card, under a smallest possible badge. Both stages are laid out, with sources, in how to reduce image file size.
Fix the scan before you compress it
Stage two is where signatures turn ragged, so make stage one succeed: black ink, plain white paper, shot straight down in even light, then clean the file.
- Crop to the ink. Blank paper around the signature costs bytes and carries nothing; Crop image does it in seconds.
- Go grayscale. A yellow or gray cast is color data the JPEG must store; the Black and white tool drops it in one click. Paper grain survives grayscale, so fix that with a bright, flat shot.
- No shadow, no flash: a phone shadow across the page is a gradient JPEG has to pay for.
- As a starting point, we suggest 400–800 px wide; if the portal states a size, use that instead.
- If PNG is accepted, try it and compare the two sizes on the cards. PNG has no quality dial, so the page skips stage one and shrinks pixels only if needed.
Rejected under 20 KB? Size was not the problem
A portal that caps the bytes may also fix the pixel dimensions, demand a .jpg extension or refuse a filename with spaces; the numbers are on its instructions page. This page shrinks by percentage and cannot land on an exact width and height, so set exact dimensions on Resize image first.
- Exact pixel size required: Resize image, then this page.
- Photo field, not a signature box: check its own limit, then use the page for that target.
- A whole signed document: send a PDF from JPG to PDF, not a loose image.
Frequently asked questions
Can this page get any image under 20 KB?
No, and it will tell you. When quality 50 does not fit, it shrinks the image in 15% steps, up to sixteen times, and at the smallest size it accepts a quality as low as 5. If the file still overshoots, the card reads smallest possible and you get that file rather than a fake success.
How bad does a photo look at 20 KB?
Expect visible loss: 20,480 bytes over a 400 × 500 px headshot is about a tenth of a byte per pixel. Open Compare and look at skin and hair. If the portal accepts more, use the 50 KB or 100 KB page; if it truly demands 20 KB for a face, crop to the head and convert to grayscale first so no bytes go to color.
Why is my scanned signature still over 20 KB?
Because of what surrounds the ink: paper grain, a yellow cast, a shadow and wide margins. Crop to the strokes, convert to black and white and generate again; the card shows the new size and whether the dimensions had to change.
The dimension tag shows an arrow and the strokes look thinner. What happened?
It means quality 50 did not get the file under 20,480 bytes at its original size, so the page shrank the dimensions 15% per pass until a quality of 50 or more fit. Look at what surrounds the ink — a gray or yellow background, a shadow, a wide margin of paper — then crop to the strokes on Crop image and generate again. This page only ever shrinks, so a downscaled result cannot be brought back up to a portal's fixed frame.
Will the card read 20 KB exactly, or less?
At or under 20,480 bytes, which the card prints as 20.0 KB. A portal that counts 20 KB as 20,000 bytes draws the line lower: anything the card shows above 19.5 KB is over it. If the upload bounces, crop closer to the ink and generate again.
PNG or JPG for a signature under 20 KB?
JPG for anything photographed. PNG only for a clean two- or three-color signature, where it is worth generating both and comparing the sizes on the cards; PNG has no quality setting, so if it does not fit the page goes straight to shrinking pixels. Check which formats the portal lists.
Is my signature uploaded anywhere during the 20 KB search?
No. Decoding, the quality search, the downscaling and the final JPEG encode all run in your browser on your own device. The output also has its EXIF block removed, so nothing the camera recorded, a GPS position included, rides along to the portal.
My scanner's black-and-white PNG is 6 KB. Why is the JPG bigger?
Because the search keeps the highest quality that fits under 20,480 bytes, not the smallest file. An input with room to spare comes back heavier, and the card shows a plus sign in front of the percentage. Both sizes pass a 20 KB rule; if the portal accepts PNG, send the original.