ICO files: a small archive of icons, and what a browser really needs
What is inside an .ico, why a PNG named .ico works as a favicon, and when you need a real one. Convert ICO in your browser, no upload.
At a glance
- Type
- Image
- Compression
- Lossless
- Extensions
- .ico
- MIME type
- image/x-icon
- Also known as
- favicon
An ICO file is not a single image but a small archive: several versions of the same icon at different sizes — 16, 32, 48, 256 pixels — packed together so that whatever is displaying it can pick the size it needs. Windows introduced the format in 1985 and it is still how application icons, shortcut icons and installer resources are supplied.
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On the web the situation is looser. Browsers request /favicon.ico by convention, but they will happily accept a PNG payload behind that filename, and have for years. That is why so many favicon tools — including this one — write PNG bytes into a .ico file: it works everywhere a favicon is needed, and a browser canvas cannot produce a genuine multi-image ICO.
The distinction matters when you leave the browser. A Windows application icon, a shortcut or an installer resource needs a real ICO with several sizes inside, and a single PNG renamed will not do. For that, a dedicated icon editor is the right tool. Converting an ICO to PNG here goes the other way and is straightforward: the icon is unpacked to an editable image, with transparency intact, and you get whichever size the browser's decoder returns — typically the largest.
Convert ICO to other formats
Convert other formats to ICO
FAQ
What size do I get converting an ICO to PNG?
Whichever the browser's decoder returns, typically the largest packed inside. To pick a specific size — especially one drawn separately rather than scaled — use a dedicated icon editor.
Is the .ico this site produces a real ICO?
No. It is PNG data in a file named .ico, which browsers accept as a favicon. A genuine multi-size ICO cannot be produced by a browser canvas.
Will that work as a favicon?
Yes. Every current browser accepts a PNG payload behind an .ico filename, and a great many sites ship their icon exactly this way.
Can I use it as a Windows application icon?
No. Application icons, shortcuts and installers need a real ICO with multiple sizes packed inside. Use a dedicated icon tool for those.
Is transparency preserved?
Yes. Icons almost always have transparent backgrounds, and PNG carries the alpha channel exactly.
Should I just use a PNG favicon?
Often, yes. Modern sites reference a .png favicon directly. The .ico name mainly serves the default /favicon.ico path that older clients still request.