Reduce Image to Exact KB
Need a photo under 500KB for a form? 200KB for an email? Type the number, done.
Drop the photo you need to shrink
JPG, PNG or WebP in, JPG out. Built for upload forms with a hard size limit.
Choose ImageHow to reduce an image to a specific KB size
Drop your image
Drag in any JPG or PNG. The file loads locally — nothing is sent to a server.
Enter target size in KB
Type the number you need — 100, 200, 500, whatever the form or upload limit requires.
Hit Reduce
The tool uses binary search to find the right quality setting that hits your target size.
Download
Check the file size matches, then save it.
Why you need a target KB tool, not just a quality slider
Most image compressors give you a quality slider and let you figure out the rest. That works fine when you just want the file to be smaller. But when you have a hard limit — a government form that rejects uploads over 200KB, an email system with a 500KB attachment cap, a job application portal that will not accept anything larger — guessing at quality settings is frustrating.
This tool takes a different approach. You tell it the target size in KB, and it runs a binary search through quality settings until it finds one that gets the file under your limit. Compress, check size, compress more or less, check again. It does all of that automatically.
The result is not always pixel-perfect to your exact number — compression does not work that way — but it gets you within a few percent of the target, which is usually close enough.
How the search finds your number
JPEG quality is a dial with no fixed relationship to file size. The same quality setting gives a small file for a plain background and a large one for a detailed photo, because the size depends on what is in the picture. That is why a target has to be searched for rather than calculated.
This tool runs the search in three stages, and stops at the first one that works.
- First it tries quality 95 at full size. If that is already under your limit, you are done and the photo keeps its best quality.
- Otherwise it runs a binary search between quality 50 and 95, halving the range each step, to find the largest file that stays at or under your limit.
- If even quality 50 is too big, it scales the photo down step by step, keeping the proportions, and searches again at each size. Scaling down is gentler on a photo than dropping quality further, which is what makes images look blocky.
Only when all of that fails does it allow quality below 50. In practice the first two stages handle most photos and the third handles large phone pictures aimed at small limits such as 20 or 50 KB.
KB can mean two different numbers
There are two definitions of a kilobyte in everyday use. Windows File Explorer counts 1024 bytes per KB. macOS Finder and most storage makers count 1000. A form that asks for a file under 50 KB may be checking 51,200 bytes or 50,000 bytes, and nothing on the form tells you which.
Aiming at the strict number means the file passes either way. The exact byte count is shown with every result, so you can check it against a form that states its limit in bytes.
When a form still rejects the file
File size is only one of the checks an upload form makes. If the size is right and the upload still fails, one of these is usually the cause.
- Pixel dimensions. Many forms ask for a specific width and height as well as a size limit. Resize to those dimensions first, then reduce to the KB limit, in that order.
- A minimum size. Some forms set a range, such as between 20 and 50 KB. If your result is below the minimum, start again from a larger or less compressed original.
- The file extension. A few validators accept .jpg but not .jpeg, or the other way round. Renaming the extension is safe because both are the same format.
- Format. This tool always produces JPG, which is what almost every photo upload form expects.