Compress Image to KB — Set Any Target File Size From 10KB to 999KB
File size limits are arbitrary, but they're enforced strictly. A job application portal that says 200KB maximum won't tell you which quality setting to use in Photoshop to hit it. A real estate listing platform capped at 500KB per image doesn't explain how to get your 3.2MB agent headshot down to spec. The MB to KB compressor skips the guesswork — you type the target, the tool finds the highest quality JPEG that fits under it.
How the target-size algorithm works
The compressor iterates through quality levels from 0.92 down to 0.04 in 0.04 increments, testing each output against your target byte count. The first quality level that produces a file at or below your target is used, which means you always get the best possible quality within the constraint. If the image encoded at 0.92 quality is already under your target — which happens when you set a generous limit like 500KB for a small image — that high-quality version is what you download.
If even quality 0.04 produces a file larger than your target (which happens with very large images and very tight targets), the algorithm scales the image down to 90% of its dimensions and starts the quality sweep again. It repeats this at 80%, 70%, 60%, and further until the target is met. The scaling is proportional, so aspect ratio is preserved throughout. The output is always the smallest dimensioned, highest quality JPEG that fits under your specified file size.
Common target sizes and what they're used for
Different platforms and use cases have settled on different file size conventions. 50KB is a common ceiling for profile photos on government and institutional portals — similar to the 20KB passport photo requirement but slightly more generous. 100KB is the sweet spot for email attachment photos and compressed social media images that still look good. 200KB works well for blog post inline images where bandwidth matters but quality is important. 500KB is the typical ceiling for print-quality web images and product photos on e-commerce platforms.
The slider goes from 10KB to 999KB because those are the boundaries where custom targeting is genuinely useful. Below 10KB, image quality degrades so severely that the output is barely usable for anything other than thumbnails. Above 999KB (1MB), general-purpose quality compression is more appropriate than a byte-count target — you'd use the image compressor for that instead. If you specifically need exactly 20KB for a passport photo or government form, the dedicated compress to 20KB tool is optimized for that workflow. For straightforward dimension changes, the image resizer handles width and height independently of file size targets.
Why the output is always JPEG
JPEG is the right format for a byte-count targeting tool because it has the most predictable and controllable compression curve of any format supported by the browser's Canvas API. WebP can sometimes achieve smaller files at equivalent quality, but its size at a given quality level is less predictable because the VP8 encoder's behavior varies more with image content. PNG is lossless — you can't hit an arbitrary byte count target with it unless you also drastically reduce dimensions. JPEG's quality-to-size relationship is consistent enough that iterating through quality levels reliably lands close to any given target.
The processing runs entirely in-browser using the HTML5 Canvas toBlob API. Your images are never uploaded to any server. For a 5MB smartphone photo being compressed to 100KB, the whole process typically takes under two seconds. Batch compression is supported — select multiple images, set your target once, and download everything as a ZIP.
When quality at your target size isn't acceptable
Tight targets and large images sometimes produce outputs that look visibly compressed even at the tool's highest achievable quality. If a 4000×3000px photo needs to fit into 50KB and the result looks blocky, the issue isn't the compressor — it's physics. You're trying to pack too many pixels into too few bytes. The fix is to reduce dimensions before compressing: use the image resizer to scale the photo to 1200×900 or 800×600 first, then run the MB to KB compressor. Smaller dimensions mean the same byte budget buys you much higher quality per pixel — a 1000×750 image at 50KB looks acceptable, while a 4000×3000 image at the same file size looks heavily degraded. For images that already have correct dimensions but just need to meet a file size ceiling, this tool is the right starting point. If you need to convert the output format or do further adjustments, the photo editor handles both.