What Is an ICO File?
ICO is the format for favicons and Windows icons. Learn what it is, why it bundles several sizes, and how to make one from your logo.
ICO is the icon format browsers and Windows use, bundling several sizes in one file so an icon stays sharp everywhere it appears.
How it works
The short answer
ICO is the icon format used by browsers for favicons and by Windows for app and file icons. It bundles several image sizes into one file so the icon looks right at any scale. Modern browsers also accept PNG, but ICO remains the classic choice.
Why ICO bundles sizes
An icon is shown at many sizes, from a tiny browser tab to a large desktop shortcut. An ICO file stores multiple versions, typically 16, 32 and 48 pixels, so the right one is always used instead of stretching a single image.
The favicon connection
Websites use a favicon in ICO or PNG format to show a small icon in the browser tab. Generating a proper favicon set from your logo is the first polish step for any site, and it is also what users see in bookmarks and history.
ICO vs PNG
PNG is a general purpose format that modern browsers accept as a favicon and is simpler to create. ICO bundles multiple sizes in one file and is required for classic Windows icons. For broadest support, deliver both from one source image.
When you need ICO
You need an ICO for a Windows shortcut, a classic favicon, or any icon system that expects the format. Modern web use can get by with a PNG, but generating an ICO too keeps every environment covered.
How to make an ICO
Start with a square image, crop it to a centered square, and export a favicon set. The favicon generator here creates the multi-size ICO plus PNG sizes, all in your browser, so nothing is uploaded.
Frequently asked questions
What is an ICO file?
ICO is the icon format used for favicons and Windows icons. It bundles several image sizes in one file.
What sizes does a favicon need?
16, 32 and 48 pixels for the ICO, plus 192 and 512 for Android home screens and app icons.
Do browsers still use ICO?
Yes, ICO is still the classic favicon format, though modern browsers also accept PNG favicons.
What image should I start from for an ICO?
A clean square source at 256 by 256 or larger gives the sharpest result when scaled down to every icon size.