ICO file format: what it is and how to use it

ICO is the Windows and favicon icon container: several sizes and bit depths of one image in a single file. Learn when to use it and what to choose instead.

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What is a ICO file?

An .ico file is an icon in the Windows icon container, a directory of image entries, each a different size and bit depth (16×16 to 256×256, old BMP-style DIBs or embedded PNGs), so the OS or browser picks the sharpest rendition. It is the format of .exe icons, desktop shortcuts and the web's favicon.ico that browsers still request by default.

When should you use ICO?

  • Favicons: favicon.ico remains the universal fallback browsers fetch.
  • Windows icons: app, file-type and shortcut icons on Windows.
  • Multi-size packaging: one file holding every resolution needed.

When is another format a better fit?

On macOS the equivalent is ICNS; for cursors, the sibling CUR. Modern web icons can be single PNG or SVG files, crisper and simpler. And never author in .ico: make the PNG master, then generate the container.

The short version: ICO is the multi-size icon box for Windows and favicons: package into it, do not draw in it.

How to open a ICO file

On Windows

Double-click the file, or open it with IcoFX.

On macOS

GIMP opens ICO files on macOS.

In your browser

Open ICO files right in a browser tab or with the dexrr viewer. No install, no upload.

Also opens in

  • Any web browser
  • GIMP
  • IcoFX
  • Paint.NET

View or convert ICO files

A quick preview or a new format. No install, no upload.

View ICO files Preview and inspect ICO files Convert to ICO Turn files into ICO ICO to CUR Windows Cursor ICO to ICNS Apple Icon Image ICO to PNG Portable Network Graphics ICO to BMP Windows Bitmap

ICO technical details

Full name
Windows Icon
Extensions
.ico
MIME type
image/vnd.microsoft.icon, image/x-icon
Magic bytes
00 00 01 00
Compression
Lossless
Developer
Microsoft

ICO questions, answered

How do I open a .ico file?

Windows shows it as the icon itself; GIMP, Paint.NET, icon editors and browsers all open it. dexrr displays and converts ico files directly in your browser.

Can I convert ICO files online?

Yes, dexrr converts ico locally in your browser: ICO to PNG to extract artwork or PNG to ICO for favicons and app icons.

Is ICO better than PNG?

For icons and favicons it is still required: one .ico serves every size. For single images, PNG is simpler and smaller; browsers accept both today.

Why is my favicon.ico blurry?

It probably holds only one large size that the browser shrinks. Pack dedicated 16×16 and 32×32 renditions into the file.

Is the ICO format outdated?

Old but required: favicon.ico is still a web convention every browser honors, and Windows still uses it everywhere.