Format at a glance
- Full name
- Microsoft Icon File
- File extensions
- .ico
- MIME types
- image/x-icon
- Category
- Images
- Compression
- Depends on the contained codec
- Transparency
- Yes
- Animation
- No
- Properties
- Alpha channel, Image sequences
Suitable tools
What is this format?
The ICO header points to individual image resources. Older entries use a BMP-like structure, while modern large icons are commonly embedded as PNG.
Transparency can use masks or alpha channels. A single visible preview does not necessarily show every included size.
What is it used for?
- Windows application and file icons
- Website favicons
- Shortcuts and desktop resources
- Icon packages containing multiple resolutions
Which programs can open it?
- Windows File Explorer
- GIMP and Krita
- IcoFX and Greenfish Icon Editor
- Browsers for favicons
Support across devices and browsers
Windows Photos or specialist image software opens ICO, sometimes with an extension.
Preview, Quick Look and image editors support compatible ICO files.
GIMP, Krita, ImageMagick and desktop viewers handle ICO depending on installed libraries.
Gallery and editing apps support ICO depending on the system version.
Photos, Files and image applications open supported ICO variants.
Native display and Canvas decoding depend on the browser; LocalFileLab uses local decoders when necessary.
Advantages
- Multiple sizes in one file
- Transparency and high-resolution PNG entries
- Native integration with Windows and browser favicons
Disadvantages
- Different internal image variants
- Not every editor exports complete size sets
- Unsuitable as a general-purpose image format
Comparison with alternatives
PNG stores one raster image; ICO can bundle several PNG or BMP representations.
SVG scales without fixed sizes but is not accepted directly as a Windows icon everywhere.
BMP may appear inside ICO but does not provide a multi-size container by itself.
LocalFileLab support
ICO is recognized as an input. Image data is read locally through browser or WebAssembly decoders.
ICO is available as a local output; available settings depend on the format.
LocalFileLab can compress ICO locally or package it in a supported archive; already compressed content will not necessarily become smaller.
A local preview is available when the browser can display or play the content.
Complete preservation of format-specific metadata is not guaranteed.
Related formats
Frequently asked questions
Which sizes should an ICO contain?
Typical sets range from 16×16 to 256×256 pixels. Required sizes depend on the application and target system.
Can ICO contain PNG?
Yes. Since Windows Vista, large compressed PNG entries have been common in ICO files.
Is ICO the same as a favicon?
ICO is one possible favicon format. Modern websites can also declare PNG or SVG icons.