Website favicons
ICO is the standard format for the favicon displayed in browser tabs, bookmarks, and address bars for websites.
Format Encyclopedia
ICO File Format
ICO is a widely used image file format with broad support across tools and platforms.
Format authority
Image format reference
MIME type: application/octet-stream
Extension: .ico
Category: image
Supported OS: Windows, macOS, Linux, iOS, Android
Quick answer
What is ICO?
ICO — Icon file format used for application icons, favicons, and desktop shortcut images, storing multiple resolutions in a single container.
ICO is an image file format. Icon file format used for application icons, favicons, and desktop shortcut images, storing multiple resolutions in a single container. It is commonly used in workflows that require reliable image handling and is supported by a wide range of applications and online tools.
Use cases
Common uses of ICO
Windows application icons
ICO is the native icon format on Windows, used for executable files, desktop shortcuts, folders, and taskbar icons.
Multi-resolution icon containers
ICO files store multiple icon sizes (16x16 to 256x256) in a single file so the OS automatically uses the most appropriate resolution.
Browser tab and bookmark icons
Browsers request favicon.ico automatically from the website root and display it in tabs, bookmarks, and history entries.
Desktop shortcut and system graphics
ICO is used for custom desktop shortcut icons on Windows, giving applications and files a recognizable visual identity on the desktop.
Comparisons
ICO vs other formats
ICO vs PNG
ICO stores multiple icon resolutions in a single container optimized for Windows and browser favicons, while PNG is simpler and preferred for single-size modern web favicons.
ICO vs SVG
ICO is a raster container optimized for Windows and multi-resolution browser favicons, while SVG is a resolution-independent vector format preferred for scalable icons on modern devices.
ICO vs BMP
ICO is a specialized icon container with multi-resolution support and transparency, while BMP is a simple uncompressed raster format without icon-specific features.
Overview
Format summary
History
ICO has a long history as a practical file format in its category.
Specification
ICO is defined by an established file specification and is widely documented by the format community.
Developer
ICO is maintained through its standardization body and broad ecosystem support. Open formats are often improved by community contributors and software vendors.
Technical details
File format characteristics
Compression
Compression behavior varies by file content and encoder settings.
Encoding
Encoding depends on the format family and standard codec definitions.
Metadata
This format carries metadata in its standard container or file headers.
Performance
Smaller files open faster and are easier to transfer.
Best practices
How to use this format well
Keep originals
Save a copy of the original file before converting or editing.
Use compatible tools
Choose software that explicitly supports the format for best results.
Advantages
Why use this format
Wide support
ICO is supported by many applications and services.
Interoperability
The format is recognized across platforms and workflow tools.
Disadvantages
Format limitations
File size
Some formats can produce large files depending on quality settings.
Format complexity
Advanced features may not be supported by every tool.
FAQ
Frequently asked questions
ICO is a file format used in image workflows.
Most modern applications in the category support this format.
Yes, it is designed for cross-platform use and broad compatibility.
Yes, many tools can convert it to other related file formats.
Use a compatible viewer or editor for the format.
Metadata handling depends on the format and the tool used.
Related formats
Related Format Guides
Related converters
Conversion tools for this format
JPG to ICO
Convert JPG images to ICO format for favicon and icons.
PNG to ICO
Convert PNG images into ICO format for website and application icons.
WEBP to ICO
Convert WEBP images to ICO format for favicon and icons.
Troubleshooting
Common problems and fixes
Check the extension
Confirm the file uses the correct extension and file header.
Try a different tool
Use another application if the current tool cannot open the file.
Reference