Convert PNG to ICO

An ICO is a folder, not a picture

An .ico file is a tiny directory: a short header, then one entry per image recording its width, height, colour depth and where its data begins. The images inside are independent, which is the entire point — Windows picks the size closest to what it needs and uses it directly, rather than shrinking a big one on the fly. That is why a real multi-size icon looks crisp in the taskbar and a single 256px image squeezed into an .ico looks like mush at 16 pixels.

The sizes offered here — 16, 32, 48 and 256 — are the ones Windows actually asks for: 16 for the title bar and small lists, 32 for the desktop and taskbar, 48 for Explorer's medium view, and 256 for the large icon views and the high-density displays that scale them. Each is rendered separately from your source at its own size rather than being derived from the one above it, so the small ones get the full quality of the original rather than the accumulated softness of successive shrinks.

256 is the ceiling and it is a property of the format, not a limit chosen here — the directory entry stores each dimension in a single byte, and a zero there means 256. Nothing larger can be described. Since Windows Vista the entries may hold PNG data rather than raw bitmaps, which is what keeps a 256px icon from occupying a quarter of a megabyte on its own and what allows proper transparency; every size here carries a full alpha channel.

A non-square source is centred on a transparent square and padded, never stretched. A wide logo squashed into a square is the most recognisable mistake an icon can make, so the shape is preserved and the spare room left empty. If you want a tighter framing, crop it to square first — the tool cannot guess which part of a rectangle matters.

When you want something else

The real difficulty with icons is not the format, it is the design. Artwork that reads beautifully at 256 pixels frequently becomes an unreadable smudge at 16, because at that size you have a shape and two colours and nothing else. Professional icon sets are drawn separately for the small sizes, with details removed and strokes thickened — no automatic reduction substitutes for that, and the preview here is honest about it so you can see the problem before shipping it.

For scripting or for a folder of icons, ImageMagick builds a multi-size file in one command: magick logo.png -define icon:auto-resize=256,48,32,16 favicon.ico. If the icon is for a website rather than an application, an .ico alone is no longer the whole answer — modern browsers, iOS home screens and Android launchers each want different files, which is what the favicon set produces.