What is ICO, exactly?
ICO is the Windows icon format— and crucially, it's a container, not a single picture. One .icofile can hold several images at once, each at a different size and color depth. When Windows or a browser needs an icon, it reaches into the file and pulls out the variant that fits the slot best: a tiny 16px version for a browser tab, a larger one for the desktop. PNG can't do that — a PNG is exactly one image at one resolution.
PNG vs ICO at a glance
| Feature | PNG | ICO |
|---|---|---|
| Type | Single image | Icon container |
| Sizes per file | One | Many (16, 32, 48...) |
| Transparency | Full alpha | Full alpha |
| Compression | Lossless | Lossless |
| Favicon support | Modern browsers | Universal, incl. legacy |
| Best for | Web graphics, app icons | favicon.ico, Windows icons |
How does a favicon.ico bundle multiple sizes?
A typical favicon.ico contains three images in one file — 16x16, 32x32, and 48x48 pixels — each its own self-contained bitmap. That matters because the same favicon shows up in very different places: a 16px tab, a 32px bookmark, a larger taskbar tile. Rather than scaling one image and getting a blurry result, the system reads the size that matches the slot. Designing each size by hand (instead of downscaling) keeps small icons crisp, since fine detail rarely survives automatic shrinking.
Don't modern browsers accept PNG favicons?
They do. Every current browser honors a PNG declared with <link rel="icon" href="...png">, and PNG is often the easier path for high-resolution and themed icons. But two things keep favicon.ico relevant: browsers still auto-request /favicon.ico from the site root even with no link tag, and a single ICO bundles every size in one request. The common pattern is to ship both — PNG links for modern browsers, plus a favicon.ico as the universal fallback that never fails.
When should you use each?
Reach for ICO when you need a classic favicon with the broadest possible support, or genuine Windows application and shortcut icons. Reach for PNG for essentially everything else — web graphics, app icons on other platforms, and larger touch icons. For a deeper dive into picking icon formats, see the best image format for icons, and for the format itself, read what an ICO file is.
How do you convert between PNG and ICO?
Start from a square, high-resolution PNG and you can generate a multi-size favicon in seconds with PNG to ICO. Going the other way — pulling an editable image out of an existing icon — use ICO to PNG. Both run entirely in your browser, and you can find every converter on the tools page.
Frequently asked questions
- Do I still need a favicon.ico in 2026?
- It's the safest default. Browsers automatically request /favicon.ico, and a single .ico bundling 16, 32, and 48px renders crisply everywhere — including older browsers that ignore PNG favicon links.
- Can I use a PNG as my favicon instead of ICO?
- Yes. Every modern browser accepts a PNG declared with a <link rel='icon'> tag. Many sites ship both: PNG icons for modern browsers and a favicon.ico as the universal fallback.
- What sizes go inside a favicon.ico?
- Commonly 16x16, 32x32, and 48x48 pixels, all packed into one file. The browser or OS picks whichever size best matches where the icon is displayed.
- Is ICO a lossy format?
- No. ICO is a container that usually stores lossless bitmap or PNG-encoded images, so quality is preserved. Its limitation is purpose, not compression — it's an icon format, not a general image format.