Build a Favicon or App Icon, Entirely in Your Browser
This tool never sends your image anywhere — everything happens locally using your browser's built-in Canvas API. An ICO file isn't just one image: it's a small container that can hold several sizes of the same icon at once, so Windows and browsers can each pick whichever one fits the space they have. Tick the sizes you want and this tool builds a single .ico file containing all of them, with transparency intact.
Under the hood, this tool embeds a full PNG image for every size inside the .ico file, rather than the older raw-bitmap format some generators still use for small icons. That's been supported by Windows since Vista (2007) and by every current browser, so there's no real compatibility tradeoff — and it means every size in your icon keeps PNG's exact, lossless quality and transparency.
What sizes should my ICO file contain?
For a website favicon, 16×16, 32×32, and 48×48 cover the common cases: 16 shows up in browser tabs, 32 on high-resolution displays and in the Windows taskbar, and 48 for desktop shortcuts. Adding 256×256 is worth it if the same file doubles as an application icon, since Windows shows icons at that size in large-icon folder views. There's no real downside to including a size you don't end up using beyond a slightly larger file, so the defaults here cover most projects.
Does converting to ICO preserve transparency?
Yes. ICO supports a full alpha channel, so transparent areas in your PNG stay transparent in every size of the resulting icon. If your source image isn't square, transparent padding is added to the shorter side by default so the icon isn't stretched — switch to the crop option instead if you'd rather fill the square and trim the overflow.
Why can't an ICO icon be larger than 256×256?
The ICO format stores each image's width and height in a single byte, which only reaches 255 — when 256×256 icons were introduced, the unused value 0 was repurposed to mean 256 rather than changing the file layout. That makes 256×256 the largest size the format itself can describe, not a limit this tool imposes. If you need a larger image, convert to a plain PNG or JPG instead of an icon.
Is there a file size or dimension limit?
No hard limit from this tool — since everything happens in your browser instead of on a server, your device's own memory is the real ceiling, not a number we've imposed. Selecting every size at once on a very large source image will take a little longer to process, but there's nothing built in that caps file size or dimensions.
Related tools
Need a plain image instead of an icon? Use the PNG to JPG Converter or the PNG to WebP Converter to convert your PNG to another everyday image format.
Last reviewed: August 2026