ICO Converter
ICO is the Windows and browser icon format, and unusually it holds several resolutions in one file so the system can pick whichever fits a tab, a taskbar or a desktop tile. Because entries are square, the useful step is choosing what survives the crop.
ICO at a glance
| Full name | Icon File Format |
|---|---|
| Extension | .ico |
| MIME type | image/x-icon |
| Compression | Lossless |
| Transparency | Yes |
| Animation | No |
| Colours | 16.7M (24/32-bit) |
| Browser support | All browsers (favicon) |
| Typical use | Website favicons, Windows application icons |
| Introduced | 1985 |
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ICO questions
What sizes should a favicon ICO contain?
16, 32 and 48 pixels covers browser tabs, bookmarks and Windows shortcuts, and adding 256 covers large desktop icons. A single ICO holds all of them and the system picks whichever fits, which is what the format exists for.
Do I still need favicon.ico if I have a PNG favicon?
It is still worth having. Browsers request /favicon.ico by default, and some tools, feed readers and older browsers look for nothing else. Modern browsers prefer a declared PNG or SVG when one is offered.
Why does my icon look blurry in the browser tab?
Usually because a single large image is being scaled down to 16 pixels, where fine detail turns to mush. An ICO containing a purpose-drawn 16-pixel version is sharp because nothing is being resized.
Can an ICO file be non-square?
The format permits it, but every system that consumes icons expects squares and will letterbox or stretch anything else. Crop to a square before converting rather than discovering what a particular platform does with the difference.