How to Resize an Image to 100 KB (or Any Target File Size)

To resize an image to 100 KB, open FileReadyNow's free Image Resizer, add your image, choose the File Size mode, pick 100 KB and click Resize. The tool works in your browser and keeps adjusting the image until it lands close to the size you asked for. The same steps work for 50 KB, 200 KB, 500 KB or 1 MB.

This guide explains what actually decides a file's size, walks through each step, and covers what to do when the result is not quite what an upload form wants.

What decides an image's file size

Three things drive the size of an image file: how many pixels it contains, which format it is saved in, and, for lossy formats, the quality setting. A photo straight from a modern phone has a lot of pixels, so it is usually far bigger than a form upload field wants.

The format matters because formats treat data differently. According to MDN's guide to image file types, JPEG is lossy while PNG is lossless, and PNG is better suited to screenshots, diagrams and line art. Lossy formats can throw away detail you are unlikely to notice to make the file smaller. Lossless formats keep everything, so they resist shrinking.

Step by step: resize an image to a target file size

1. Open the tool and add your image. Go to the Image Resizer and select a file or drag it in. It accepts JPG, PNG, WEBP and GIF, up to 20 MB per file, and you can add up to 10 files at once. BMP and TIFF are not supported, and for a GIF only the first frame is kept.
2. Choose File Size. The modes are Pixels, Percent, File Size and Presets. Pick File Size.
3. Set your target. Enter a value in KB or MB, or use the quick picks: 50 KB, 100 KB, 200 KB, 500 KB and 1 MB.
4. Check the options. Aspect ratio lock is on by default, so the image keeps its proportions. If your image is already smaller than the target, tick the option that stops the tool from enlarging it.
5. Click Resize. The tool page says it runs up to 12 passes, narrowing in until the output lands within 5% of your target.
6. Download and check. Save the result, then look at its size in your file manager. Open the image at full size to make sure it still looks acceptable.

Aim a little under a hard limit

Because the tool lands within 5% of the target, it will not always hit the number exactly. If a form says the file must be under 100 KB, do not set the target to exactly 100 KB. Set it a little lower, such as 90 KB, then confirm the downloaded file size before you upload it. It is a small habit that saves a rejected upload.

Choosing the output format

The Image Resizer lets you keep the original format or switch to JPG, PNG or WEBP, and the quality slider applies to JPG and WEBP. If you start with a large PNG photo and the result is still bigger than you need, try switching the output to JPG or WEBP and run it again. Here is how the formats compare for this job.

If all you need is to change a PNG into a JPG, the PNG to JPG converter does that directly.

Pixels or file size: which mode should you use?

Use File Size when a form, email system or website gives you a maximum in KB or MB. Use Pixels when the requirement is a width and height, such as a profile picture that must be a certain dimension. The Presets mode covers common platform sizes. Some uploads ask for both, and in that case resize by dimensions first, then run the File Size mode on the result.

Resizing on a phone

The tool page says it works in a mobile browser, with no app to install, so you can resize on an iPhone or any phone with a browser. Pick the photo from your gallery when the upload prompt appears, then follow the same steps.

What about PDFs?

This guide is about images. If the thing you need to shrink is a PDF, use the PDF Compressor instead. Note that it works differently from the Image Resizer, because its page says it uploads your file to a server to process it.

A note on privacy

The Image Resizer page says files are processed entirely in your browser and never leave your device. That is the site's own statement, and you can check it yourself. Open your browser's developer tools, go to the Network tab, clear the log, and resize a harmless test image. Small page and analytics requests are normal. A large request carrying your image to the site would be the sign of an upload.

Image file size questions, answered

How do I resize an image to 100 KB?

Open FileReadyNow's Image Resizer, add your image, choose the File Size mode, pick 100 KB from the quick options, and click Resize. Then download the result and check its size in your file manager. If the form states a hard maximum, aim slightly below it to leave some room.

Can I get an exact file size?

Not to the byte. The tool page says it runs up to 12 passes and lands within 5% of your target. If a form says the file must be under 100 KB, set the target a little lower, such as 90 KB, then check the downloaded file before you upload it.

Does reducing file size reduce image quality?

Usually some detail is lost, especially for large reductions. The tool page says it aims to keep visible loss low. Fewer pixels and lower quality both shrink a file, so look at the result at full size and rerun with a slightly higher target if it looks too soft.

Which format gives the smallest file?

For photos, JPG and WEBP are the usual choices because they are lossy formats that can trade a little quality for a smaller file. PNG is lossless, so it often stays larger. MDN notes that WebP can compress better than JPEG, though support is more limited.

Is my image uploaded when I resize it?

The Image Resizer page says files are processed entirely in your browser and never leave your device. You can check this yourself by watching the Network tab in your browser's developer tools while you resize a test image. Small analytics requests are normal.

Ready to try it? Open the Image Resizer, choose File Size, set your target a little under the limit, and check the downloaded file before you upload it.