ICO Format — What is Icon File Format?
ICO is the standard icon format for Windows and web favicons. It can contain multiple image sizes and color depths within a single file.
Extension
.ico
Compression
Lossless
Transparency
Yes
MIME Type
image/x-icon
Pros & Cons
✅ Pros
- • Multiple sizes in one file
- • Favicon standard
- • Transparency support
- • Windows icon standard
❌ Cons
- • Limited to small sizes
- • Windows-centric
- • Not for general images
- • Complex structure
Best Use Cases
- Website favicons
- Windows application icons
- Desktop shortcuts
- Browser tab icons
Technical Details
ICO files use a directory structure that can contain multiple BMP or PNG images at different sizes (16x16, 32x32, 48x48, 256x256). Modern ICO files often embed PNG data.
History
ICO was introduced by Microsoft with Windows 1.0 in 1985. It remains the standard format for favicons on the web and Windows application icons.