Reduce Image Size in KB

How to reduce an image to a size in KB

1. Choose or drop the image — a photo, a scanned signature, a document scan. Several at once is fine; each is reduced with the same settings.
2. Pick the maximum size the form allows: 10, 20, 50, 100, 200 or 500 KB, or "Other size" for any number.
3. If the form fixes the width and height in pixels, choose "Exact width × height" and enter them. Otherwise leave "Keep proportions": the picture keeps its shape and is made smaller only when the limit requires it.
4. Download the JPG. The result shows its size, its width and height, and the JPG quality that was used.

Read the form's requirements first

Online application forms — exams, jobs, scholarships, visas, bank and ID paperwork — usually spell out what an upload must look like: the file type (almost always JPG or JPEG), a maximum size and often a minimum size in KB, sometimes the dimensions in pixels or centimeters, and rules for the photo itself such as background color or how recent it must be. Every form sets its own values and they change from year to year, so check the current notice and follow it exactly. This tool takes care of the file size and the dimensions; the photo rules are up to you.

If a notice gives the size in centimeters only, what usually matters is the shape: 3.5 × 4.5 cm is a 7:9 portrait. Pixels follow from the print resolution — at 300 dots per inch, 3.5 cm (1.38 inches) is about 413 pixels — so use pixel values only when the form states them or tells you the resolution.

How it works

Your browser draws the image and saves it as a JPG. The size of a JPG grows with its quality setting, so the tool searches for the highest quality that still fits: it tries 75%, then 88% or 62%, halving the range each time, and after about six tries keeps the best result under the limit. With "Keep proportions" the search never goes below 50% quality. If even 50% is too big, the picture simply has more pixels than the limit can hold — lowering the quality further would make it blotchy — so the tool reduces the dimensions instead. A JPG's size roughly follows its number of pixels, so the width and height are multiplied by the square root of (limit ÷ size), with a 5% safety margin, and the quality search runs again at the new size.

With "Exact width × height" the dimensions can't change. The middle of your picture is cropped to the form's shape and scaled to exactly those pixels — nothing is stretched — and only the quality is searched, down to 10%. If the result still doesn't fit, the tool tells you how small it could get.

Is 1 KB 1,000 or 1,024 bytes?

Both are in use: Windows File Explorer counts 1 KB as 1,024 bytes, macOS Finder as 1,000 bytes, and websites follow either rule. To be safe both ways, the tool keeps every file under the limit times 1,000 bytes — a "50 KB" result is at most 50,000 bytes, which is 48.8 KB in 1,024-byte units. Sizes on this page are shown the Windows way, in 1,024-byte KB, next to the exact number of bytes.

Worked example

Say a form asks for a photo of 350 × 450 pixels under 50 KB, and your phone photo is 3,024 × 4,032 pixels. Choose 50 KB and "Exact width × height", then enter 350 and 450. The photo is a 3:4 rectangle and the form wants 7:9, which is slightly wider, so the tool keeps the full width and trims 72 pixels from the top and from the bottom (4,032 − 3,888 = 144 in all), scales what remains to 350 × 450, and searches for the highest quality under 50,000 bytes.

Without fixed dimensions, a 20 KB limit works differently. If the photo at full size and 50% quality came to 1,000,000 bytes, the tool would scale it by √(20,000 ÷ 1,000,000) × 0.95 ≈ 0.134 — to about 542 × 406 pixels for a 4,032 × 3,024 photo — and search the quality again at that size. The result shows the exact numbers for your picture.

Tips

• Signatures: sign on plain white paper with a dark pen, photograph it in good light from straight above, and crop it close to the signature before reducing it, so the pixels go to the ink rather than the empty paper.
• Start from the original photo each time. Re-saving an already-reduced JPG loses a little more detail on every round.
• Transparent PNGs get a white background, because JPG has no transparency.
• Need control over quality or format rather than a size limit? The image compressor lets you set the quality yourself and save as WebP, and the image resizer changes dimensions by percent, width or exact size.

Your photos stay on your device

The images people shrink for forms are personal by nature: faces, signatures, ID cards and certificates. Here they are processed by your own browser and never uploaded, and the JPG you download is a freshly drawn image without the original's hidden metadata such as the camera model or the GPS location of the photo. To combine several reduced images into one document, use JPG to PDF.

Frequently asked questions

Last updated: October 15, 2026