Which one do I need?
- The form gives a maximum in KB (for example "not more than 50 KB"): use reduce image size in KB and type the number, or open the page for the common sizes: 20 KB, 50 KB, 100 KB or 200 KB. Each size page explains what usually goes in that size and how to get the best result.
- The form says the file is too small (a minimum such as "at least 10 KB"): use increase image size in KB. It raises the quality first and the pixel size only if needed.
- The form gives a size in cm, mm or inches (for example a 3.5 x 4.5 cm photograph): use the image resizer in cm, which also writes the DPI into the JPG.
- The form gives both, such as 200 x 230 pixels and 20 to 50 KB: any of the tools takes a width and height as well as a KB limit.
What happens to your image
Nothing is uploaded. The page reads the image you choose, redraws it at the size you set and saves it as a new JPG, PNG or WebP, all inside your browser. On most phones and computers this happens in a background worker so the page stays responsive. The only requests the page makes while you work are tiny counters that carry an event name such as img_compress_success, never the image, its name or its size. How to check this yourself.
The saved copy is a fresh image, so it does not carry the camera details or location that phones store inside photos. The original on your device is not changed.
Limits
Each image can be up to 25 MB, and up to 30 images can be done at once with one setting. JPG, PNG, WebP and AVIF open in all current browsers. HEIC photos from an iPhone open in recent versions of Safari on iPhone and Mac; other browsers cannot read HEIC, so save the photo as JPG first or pick it from the Photos library, which usually hands the page a JPG. Very large photos are worked on at up to 16 megapixels, to stay within the canvas limit of iPhone browsers.