What is .ico?
ICO is an image file format for computer icons in Microsoft Windows. Unlike standard image formats, a single .ico file can contain multiple images at different sizes and color depths, allowing the operating system to scale the icon appropriately.
This quick guide explains when to use .ico files, how to open them on any device, and how to share them instantly with FileXhost.
When to use .ico files
- You are creating a `favicon.ico` for a website (essential for browser tabs).
- You are designing an icon for a Windows application executable (.exe).
- You need an image that scales crisply from 16x16 up to 256x256 pixels.
How to open .ico files
ICO files can be viewed in standard image viewers (Windows Photos, Preview on macOS) and edited in image editors like GIMP, Photoshop (with plugin), or online icon generators.
Algorithm details
An ICO file consists of a directory header that lists the images it contains, followed by the image data itself. The images can be raw BMP data or PNG-compressed data (introduced in Windows Vista for 256x256 icons).
Browser & platform support
- Favicon: Supported by all browsers as the standard `favicon.ico`.
- Display: Most modern browsers can display .ico files directly.
Format comparison
| Feature | Details |
|---|---|
| Multi-size | Unique ability to store 16x16, 32x32, 48x48, etc., in one file. PNG/JPG only store one size. |
| Transparency | Supports binary (on/off) transparency or full alpha channel transparency (like PNG). |
| Web Use | Standard for favicons, but PNG/SVG are increasingly used for other web icons. |
How to create ico files
- Online Converters: Favicon.io, RealFaviconGenerator.
- Image Editors: GIMP (native support), Photoshop (needs plugin).
- CLI: ImageMagick (`convert image.png icon.ico`).
How to convert ico files
- Convert to PNG: Useful if you need to edit the icon in a basic editor.
- FileXhost: Upload to host your website's favicon.
Advantages & disadvantages
Advantages
- The standard for Windows icons and web favicons
- Stores multiple resolutions in one file
- Backward compatible with very old software
Disadvantages
- Not ideal for general photography or web graphics
- Larger file size than PNG if not optimized
- Creating them requires specific tools (cannot just rename a JPG)
Tools & software
Editors
GIMP, Paint.NET, IcoFX
Generators
Favicon.io, RealFaviconGenerator
Viewers
Windows Explorer, macOS Preview
Frequently asked questions
Why do I need a favicon.ico?
Browsers automatically look for this file at the root of your site to display an icon in the browser tab and bookmarks.
Can I use PNG for favicons?
Yes, modern browsers support PNG favicons, but keeping a fallback `favicon.ico` is recommended for compatibility.
How many sizes should be in an ICO?
For web favicons, usually 16x16, 32x32, and 48x48 are sufficient. For Windows apps, include up to 256x256.
Technical specs
- File type
- Image
- Extension
- .ico
- MIME type
- image/x-icon, image/vnd.microsoft.icon
- Compression
- Uncompressed
- Max file size on FileXhost
- Typically small (1KB - 200KB). Up to 25 MB per file on free plans.
Share .ico files instantly
Upload your .ico file to FileXhost to get a clean, shareable URL in seconds. View the file in a modern browser, protect access with optional settings, and let others download it without any confusing ads or cluttered file pages.
Upload .ico file