What is an ICO file?
ICO is the icon file that Windows and browsers use, and it holds several sizes of the same picture in one file so nothing ever has to be stretched. The favicon.ico sitting at the root of a website is one of these. You can convert ICO files here, both into the format and out of it.
Specification
| Full name | Windows Icon |
|---|---|
| Extensions | .ico |
| Media type | image/x-icon |
| Compression | Lossy or lossless, depending on the mode |
| Transparency | Supported |
| Animation | Not supported |
| Multiple pages | Supported |
| Colour depth | Up to 32-bit with alpha |
| Size limits | 256 x 256 pixels per entry |
| Introduced | 1985 |
| Developed by | Microsoft |
| Standard | Proprietary |
| Browser support | Every browser, including older ones |
What ICO is used for
- favicon.ico at the root of a website
- Windows application and shortcut icons
- Installer and desktop shell resources
- Multi-resolution icon sets in a single file
Strengths and limitations
What ICO does well
- Holds several resolutions so the system never has to rescale
- Still the most reliably recognised favicon format
- Supports smooth transparency around the edges of an icon
Where ICO falls short
- Each picture inside it is capped at a small size
- Not a general purpose image format for content
- Older BMP-based entries waste a lot of space
Convert ICO to
Every target this format can be written out as, each on its own page.
Convert to ICO
Everything that can be turned into a ICO file.
Questions about ICO
What is a .ico file?
ICO is the icon file that Windows and browsers use, and it holds several sizes of the same picture in one file so nothing ever has to be stretched. The extension .ico identifies it, and its media type is image/x-icon.
How do I open an ICO file?
Any current browser will open it directly, so dragging the file into a tab is usually enough. Most operating systems also preview it without extra software.
Is ICO lossy or lossless?
Lossy or lossless, depending on the mode. Check which mode a particular file used before assuming anything about its quality.
What is ICO good for?
Holds several resolutions so the system never has to rescale. Still the most reliably recognised favicon format. Supports smooth transparency around the edges of an icon. In practice that makes it a good fit for favicon.ico at the root of a website, and Windows application and shortcut icons.
What are the drawbacks of ICO?
Each picture inside it is capped at a small size. Not a general purpose image format for content. Older BMP-based entries waste a lot of space.