How this converter works
An ICO file is not one image; it is a small container holding the same icon at several sizes, so Windows and browsers can pick the right one for a tab, a taskbar or a desktop shortcut. This tool decodes your PNG locally, redraws it at 16, 32, 48 and 256 pixels, and packs all four into one standards-correct .ico. Transparency is preserved at every size, and nothing is uploaded anywhere.
The favicon use case, start to finish
The reason almost everyone needs an ICO: favicon.ico, the icon browsers request from every website. Start from a square PNG, ideally 256 pixels or larger, with a simple shape that survives shrinking to 16 pixels; drop it here, download the ico, upload it to your site root as /favicon.ico. Browsers find it automatically with no HTML changes, and the multi-size container means the tab icon, the bookmark icon and the shortcut icon all render sharp.
What to feed it for a sharp result
Two rules cover it. Use a square image: a rectangular PNG gets centered on a transparent square rather than stretched, which is correct but wastes icon space. And prefer simple over detailed: at 16 pixels, thin lines and small text turn to mush no matter the converter, which is why the best favicons are a letter, a glyph or a bold shape. Fine details survive only in the 256 pixel entry.