Compress ICO files without losing a pixel
An ICO file holds the same icon at several sizes, from 16 pixels for browser tabs up to 256 pixels for desktops. Each size is stored either as an old-style bitmap (BMP) or as a PNG. Bitmaps aren't compressed at all: a single 256 × 256 bitmap is a fixed 256 KB or more, even for a simple logo. This tool converts large bitmaps to PNG, re-compresses existing PNGs, and lets you drop sizes you don't need. Every pixel stays exactly the same.
Everything runs in your browser. Your icons are never uploaded.
How to use it
- Choose one or more
.icoor.curfiles, or drag them onto the box. - Review the sizes inside each icon. Untick any you don't need, or use the Favicon sizes shortcut.
- Check the savings and the verification badge, then download the compressed icon.
Where the savings come from
| Image inside the icon | As a bitmap | As PNG (typical) |
|---|---|---|
| 256 × 256, 32-bit | 262 KB | 6 to 60 KB |
| 128 × 128, 32-bit | 66 KB | 3 to 18 KB |
| 64 × 64, 32-bit | 16 KB | 1.5 to 5 KB |
| 16 to 48 px | 1 to 9 KB | Kept as bitmaps by default, for compatibility |
PNG compression is lossless, so the icon looks identical. Windows Vista and later, every modern browser, and macOS all read PNG images inside icons. Small sizes stay as bitmaps by default because very old programs only understand bitmaps at those sizes. If your icon is only for the web, choose "All sizes" for the smallest file.
Choosing sizes for a favicon
Browsers use the 16 and 32 pixel images for tabs and bookmarks, and Windows uses 48 pixels for shortcuts. A favicon rarely needs anything else, so the Favicon sizes button keeps just those three, which can cut a large icon file down to a few kilobytes. Modern sites usually also provide a separate 180 × 180 PNG for Apple devices and larger PNGs in a web manifest, rather than packing big sizes into the ICO.
Verified pixel by pixel
After compressing, the tool decodes every image in the new icon and compares each pixel, including transparency, with the original. The green Verified badge means they're identical. It uses its own exact image decoders rather than the browser's canvas, which can slightly change semi-transparent pixels. PNGs inside the icon are saved as standard 32-bit RGBA images, the format Windows expects, because some icon readers mishandle other PNG types inside ICO files. During development, results were also checked with Pillow and ImageMagick, using icons made by both and real website favicons.
Frequently asked questions
Will my icon look different?
No. PNG compression is lossless, and the result is checked pixel by pixel, including transparency. Only sizes you untick are removed.
Are my files uploaded?
No. Icons are decoded, compressed, and rebuilt in your browser.
Does it work with cursor (.cur) files?
Yes. The hotspot, the point that clicks, is kept for every size. Existing PNG images are re-compressed, but bitmaps in cursors aren't converted, since some programs only accept bitmap cursors.
Why didn’t my icon get smaller?
If it already stores large sizes as well-compressed PNGs and small sizes as bitmaps, it's already efficient. Removing sizes you don't need is the remaining option.
Can I create an ICO from a PNG here?
This tool compresses existing icons. To make a new icon, use a PNG to ICO converter, then bring the result here if it's larger than expected.