Compress an Image to 100 KB

At 100 KB the encoder has 819,200 bits. For a 1200 x 800 image (960,000 pixels) that is about 0.85 bits per pixel; for 800 x 600 it is about 1.7. In practice that covers blog images, product thumbnails, form uploads that ask for "under 100 KB" and images you want to keep light in an email.

It is not a good fit for large hero banners at full desktop width or for photos people will zoom into, where you either need more bytes or a careful choice of format and dimensions.

The tool first draws your image at full size (anything longer than 4096 pixels on its long side is reduced to 4096 px) and encodes it at quality 0.8. If that file is already at or under the target (and not larger than your original), you get it straight away. If not, it repeats up to 10 times. On each pass it multiplies the quality by 0.95 (0.85 for PNG) and, because the first attempt was too big, also shrinks the width and height to 95% of the previous pass.

Ten passes is the limit. After all ten, the width and height have dropped to about 60% of where they started and the quality setting to about 0.48. If the file is still too big at that point, you get the last attempt and a note saying the target was not reached.

• WebP (the default) usually keeps more detail at a fixed size and supports transparency.
• JPG is accepted everywhere; choose it for forms and email.
• PNG only makes sense for screenshots and graphics with few colours. A photo saved as PNG under 100 KB will be heavily reduced in colours and dimensions.

Ten attempts are not always enough for very large photos. The tool shows a note when the result is still above 100 KB. Resize the image to the width it will actually be shown at (the Image Resizer or, for many files, the Bulk Image Resizer) and run it again.

Everything happens in your browser; the image is not uploaded.