Image format
The ICO format
ICO is a small container that holds the same icon at several sizes. ICO has held Windows icons since the first version of Windows, and browsers adopted it for favicons in 1999.
When to use ICO
Use ICO for a favicon.ico at the root of a website, or an icon for a Windows program or shortcut.
It is best for website favicons and Windows shortcuts, and it opens on browsers (as a favicon) and Windows.
How to open it: Drag it into a browser tab or open it in Windows Photos; most editors import ICO files.
| Full name | Windows Icon |
|---|---|
| Extensions | .ico, .cur |
| MIME type | image/x-icon |
| Introduced | 1985 |
| Compression | Lossless |
| Transparency | Yes |
| Animation | No |
| Support | Opens almost everywhere |
| Typical size | A full favicon with every size is usually under 100 KB |
Good at
- One file carries 16 px through 256 px versions
- Full transparency
Not so good at
- No use for photographs
- Nothing larger than 256 × 256 pixels
The common mistake
Renaming a PNG to favicon.ico works in some browsers and silently fails in others. A real ICO holds several sizes so each place picks the right one.
Convert ICO to another image format
Questions
What is an ICO file?
ICO (Windows Icon) is a small container that holds the same icon at several sizes. ICO has held Windows icons since the first version of Windows, and browsers adopted it for favicons in 1999.
How do I open an ICO file?
Drag it into a browser tab or open it in Windows Photos; most editors import ICO files.
How do I convert ICO to another format?
Pick the target on this page, or open the Image Converter, drop the ICO file and choose a format. It converts in your browser, so nothing is uploaded.