How to Compress an Image to an Exact KB Size (100 KB, 200 KB, 1 MB)

Upload forms love arbitrary limits. A visa application wants your photo between 20 KB and 50 KB. A university portal caps documents at 200 KB. A job site rejects anything over 1 MB. Meanwhile your phone produces 5 MB photos by default. Here is how to land on a specific number without ending up with a smeared, unusable image.

What actually drives image file size

Three factors, in order of impact:

1. Pixel dimensions. Halving both width and height removes three-quarters of the pixels. This is by far the biggest lever and the one people ignore.
2. Compression quality. The JPEG quality setting, typically 0–100. Going from 95 to 80 saves a lot and is nearly invisible; going below about 60 starts showing blocky artefacts around edges and text.
3. Format. At equal visual quality, WEBP is roughly 25–35% smaller than JPEG, and much smaller than PNG for photographs. PNG is only the right choice for flat graphics, screenshots with text, or transparency.

The recipe for hitting a target

1. Decide the largest size the image will ever be displayed at. A passport photo is printed at a few centimetres; a web banner is at most 2000 px wide. Anything beyond that is wasted data.
2. Resize to that dimension with Resize Image.
3. Open Compress Image and start at quality 80. Check the resulting size.
4. If it is still too big, drop to 70, then 60. Below 60, go back and reduce dimensions instead — softening a large image looks worse than showing a smaller sharp one.
5. If the destination accepts WEBP, convert with Image Converter for a free extra 30% saving.

Rough starting points by target

• Under 50 KB (ID photos, form portraits): 600 × 800 px, JPEG quality 70.
• Under 100 KB (profile pictures, thumbnails): 800–1000 px on the long edge, quality 75.
• Under 200 KB (scanned documents, portal uploads): 1200 px long edge, quality 75, greyscale if it is a document scan.
• Under 1 MB (web hero images, email attachments): 1920 px wide, quality 80, WEBP if allowed.

Photos of documents are a special case

A phone photo of an ID card or a certificate is mostly flat paper. Converting it to greyscale before compressing often halves the size again with no loss of legibility, because colour channels are where much of the data lives. Crop tightly to the document itself as well — the desk around it is pure waste.

For a whole folder of images, Bulk Image Compress applies the same settings across every file at once and hands back a ZIP.

Three mistakes that ruin the result

• Recompressing an already-compressed JPEG repeatedly. Each pass bakes in the previous pass's artefacts. Always start from the original when you can.
• Using PNG for photographs. PNG is lossless, so a photo saved as PNG can be five times larger than the same photo as JPEG at quality 80 with no visible benefit.
• Upscaling to meet a minimum. Some forms demand a minimum size as well as a maximum. Enlarging a small image adds pixels but no detail; re-shoot or re-scan instead.

Everything above runs locally in the browser, which matters here more than usual — ID photos and scanned documents are exactly the files you do not want sitting in a stranger's upload folder.