ICO is the icon file format for Windows — it packs multiple image sizes and colour depths into a single file so the OS can pick the right version for taskbars, desktop shortcuts, and title bars.
Safe format
Type Image
By Microsoft
MIMEimage/x-icon
Drop any file to identify it
We read file headers, not extensions. Nothing gets uploaded.
ICO is the icon file format for Windows — it packs multiple image sizes and colour depths into a single file so the OS can pick the right version for taskbars, desktop shortcuts, and title bars. Tiny squares that represent entire brands. ICO is also the original favicon format — that little icon in your browser tab. Modern websites have mostly moved to PNG or SVG favicons, but ICO remains the only format guaranteed to work in every browser, including ancient versions of Internet Explorer. If you are building a website or a Windows application, you will need one.
Technical details
Full Name
Icon File
MIME Type
image/x-icon
Developer
Microsoft
Magic Bytes
00 00 01 00
Safety
.ico is a known, safe format.
What opens it
Any web browser
FREEAll
GIMP
FREEAll
IcoFX
$60Windows
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FAQ
Should I use ICO or PNG for my favicon?
Use both. ICO for maximum compatibility (including old browsers), PNG for modern browsers. Most favicon generators produce both. You can convert between them with <a href="https://fwip.app/tools/png-to-ico/">fwip</a>.
How do I create an ICO file?
Start with a square PNG (at least 256x256 pixels) and convert it with <a href="https://fwip.app/tools/png-to-ico/">fwip's PNG to ICO converter</a>. It bundles multiple sizes (16x16, 32x32, 48x48) into one file.
What sizes should an ICO file contain?
At minimum: 16x16 (browser tabs), 32x32 (taskbar), and 48x48 (desktop). For high-DPI displays, include 256x256. A properly built ICO file contains all of these in a single file.