How the compression works
Each image is opened in your browser and saved again with stronger compression. JPG and WebP are lossy formats: the encoder throws away detail your eye is unlikely to miss, and the quality number (30 to 100) sets how much. PNG is lossless, so instead of lowering quality the tool runs it through oxipng, an optimizer that finds a smaller way to store exactly the same pixels.
In "Fit under a file size" mode the tool searches for the best quality that fits. It starts at quality 92, checks the lowest acceptable quality (35), then narrows the gap in six halving steps. If quality 35 is still too large, it scales the picture down, using the fact that file size roughly follows the number of pixels, and searches again.
Next scale ≈ current scale × √(target size ÷ current size) × 0.95
Example: 400 KB at full size, target 200 KB: √(200 ÷ 400) × 0.95 = 0.67, so about two thirds of the width and height
Worked example: a job application that wants photos under 200 KB
You have three phone photos of 3.4 MB, 2.9 MB and 4.1 MB, each 4032 × 3024 pixels. Choose "Fit under a file size", pick 200 KB, keep "Same format" and press Compress. Phone photos this size rarely get under 200 KB on quality alone, so each one is also scaled down, and the list shows something like "now 196 KB (94% smaller), 1650 × 1238, pixels reduced to fit, quality 74". Choosing "Longest side 1920 px" under "Also resize" first usually gives a sharper result at the same size, because fewer pixels need less compression.
Which format to save as
| Format | Best for | Notes |
|---|---|---|
| JPG | Photos for email, forms and websites | Opens everywhere. No transparency: clear areas turn white. |
| WebP | Photos and graphics on your own website | Google reports lossy WebP files 25 to 34% smaller than JPG at similar quality. Safari can open WebP but cannot save it, so the option is off there. |
| PNG | Screenshots, logos, images with transparency | Lossless. Big for photos. |
Privacy and limits
Images never leave your device, and EXIF data, including GPS location, is removed by default. A file already smaller than your target, in the same format, with nothing to strip, is returned unchanged. Very large images are limited to 16.7 megapixels, the most phones can draw. GIF, BMP and HEIC files are not accepted here; convert HEIC photos with the HEIC to JPG tool first.
Questions people ask
How do I get a photo under 100 KB, 200 KB or 1 MB?
Choose "Fit under a file size" and pick the limit, or type your own. The tool tries quality 92 first and lowers it step by step until the file fits. If even quality 35 is too big, it shrinks the pixel size as well, and the list tells you the quality and whether the pixels were reduced. Sizes count 1 KB as 1,000 bytes, so a file under "100 KB" also passes forms that count 1 KB as 1,024 bytes.
What quality setting should I use?
For photos, 75 to 85 is the sweet spot: files are often half the size or less and the difference is hard to see. Go higher for prints or photos with fine text, lower only for thumbnails. The quality slider applies to JPG and WebP; PNG is compressed losslessly, so the slider does not change it.
Why did a file get bigger, or stay the same?
Some images are already compressed harder than the settings you chose. When the result would be larger than the original, the tool keeps your original file and marks it "already well compressed, original kept". The exception is when you asked it to remove EXIF data: then it saves the new copy so the location data is gone, even if it is slightly larger.
Does it remove GPS location from my photos?
Yes, by default. "Remove EXIF data" is ticked, so the saved files carry no camera details, date taken or GPS position. If you want to keep that information, untick it; this works when a JPG is saved as JPG, and the rotation tag is reset so the photo is not turned twice.
Why does PNG compression not shrink my file much?
PNG is lossless: it keeps every pixel exactly, so the only savings come from packing the data more efficiently, which the optimizer (oxipng) does. For a photo saved as PNG, switching to JPG or WebP usually makes it many times smaller. Screenshots and logos with flat colors compress much better as PNG than photos do.
Are my images uploaded to compress them?
No. Every image is decoded, compressed and saved inside your browser. There is no upload, no account and no daily limit; the only limit is your device memory, about 1.5 GB of images at a time on a computer and 400 MB on a phone.