What Is an ICO File?
ICO is Microsoft’s icon file format, used by Windows since its early versions. Unlike regular image formats that contain a single image, ICO is a multi-resolution container — one .ico file can hold multiple images at different sizes and color depths.
When Windows needs to display an icon (in the taskbar, desktop, file explorer, or Start menu), it picks the most appropriate size from the ICO container. This ensures icons look sharp whether displayed as tiny 16x16 toolbar buttons or large 256x256 desktop icons.
How ICO Differs from PNG/JPG
- Multi-resolution: One ICO file contains 4–6 images at different sizes. PNG and JPG contain one image at one size.
- Purpose-built: Designed specifically for operating system icons and web favicons.
- Size selection: The OS or browser automatically picks the best size — no manual selection needed.
- Internal format: Images inside ICO can be stored as either BMP data or PNG-compressed data (supported since Windows Vista and usually used for the 256x256 image, the largest size an ICO entry can have).
ICO Sizes and Their Uses
| Size | Where It Appears |
|---|---|
| 16x16 | Browser tabs, file lists, toolbar buttons, address bar |
| 32x32 | Desktop shortcuts, taskbar icons, bookmark icons |
| 48x48 | Windows Explorer medium view |
| 64x64 | Windows Explorer tile view |
| 128x128 | macOS-style display, large icon views |
| 256x256 | Windows jumbo icons, high-DPI displays |
ICO for Web Favicons
The most common use of ICO today is as a website favicon (favorite icon). When you see a small icon in your browser tab, that is typically a favicon.ico file. Browsers automatically look for /favicon.ico at the root of every website.
A typical favicon.ico contains at least two sizes: 16x16 (browser tab) and 32x32 (bookmark bar). Well-prepared favicons also include 48x48 and sometimes 256x256 for high-DPI displays. For the full set of sizes and the HTML tags, see our guide on how to make a favicon from your logo.
ICO vs PNG for Favicons
Modern browsers (Chrome, Firefox, Safari, Edge) support PNG favicons via the <link rel="icon"> tag. However, ICO offers broader legacy compatibility:
- ICO: Works everywhere, including very old browsers and Windows OS features (shortcuts, bookmarks).
- PNG: Works in all modern browsers but may not be picked up by Windows for desktop shortcuts.
- Best practice: Provide both. Place favicon.ico in your root directory, and add PNG links for modern browsers.
How to Open ICO Files
- Windows: Native support — double-click to view in Photos
- Mac: Preview can open ICO but may show only one size layer
- Linux: Most image viewers (Eye of GNOME, Gwenview) handle ICO
- Any device: Convert to PNG using our tool for universal viewing and editing
How to Extract Images from ICO
Since ICO is a container with multiple images, you may want to extract individual sizes as separate PNG files. Our converter extracts the largest available size from the ICO file, giving you a clean PNG that you can resize as needed.
Creating ICO files? Use our PNG to ICO converter to generate multi-resolution favicon files from your logo or icon design.
How to Make an ICO File
From a PNG, online
- Start with a square PNG, ideally 256×256 or larger, with a transparent background.
- Upload it to the CleverUtils PNG to ICO converter.
- Download the .ico. It contains six sizes: 256, 128, 64, 48, 32 and 16 pixels.
GIMP
Open the image, add one layer per size you want (for example 16, 32, 48 and 256 px), then use File → Export As with a .ico name. Each layer becomes one icon size.
ImageMagick
The converter on this site runs essentially this command: convert logo.png -define icon:auto-resize=256,128,64,48,32,16 favicon.ico
Use an ICO as a Windows folder icon
- Right-click the folder and choose Properties.
- Open the Customize tab and click Change Icon.
- Click Browse, select your .ico file and confirm with OK.