Convert PNG to ICO — Multi-Size Icons

What an .ico file actually is

An .ico is not one picture but a small directory of pictures of different sizes. Windows, and browsers reading a favicon, pick the entry closest to the size they need — 16 px in a browser tab, 32 px on a high-density tab or taskbar, 48 px in Explorer, 256 px for large desktop icons. Renaming a .png to .ico does not make one; some programs will open it, many will not. This tool writes a proper icon directory with each size you tick stored as a PNG inside it, which keeps smooth transparent edges.

Which sizes to include

How big is an .ico file?

Each frame inside an .ico can be stored two ways. The original format is an uncompressed bitmap: a 40-byte header, 4 bytes for every pixel and a 1-bit transparency mask. Windows Vista added PNG frames, and Microsoft recommends PNG for 256 px icons because a raw 256 × 256 frame is about a quarter of a megabyte. Here is what each size costs uncompressed, which is the ceiling a PNG frame shrinks from:

Every frame this converter writes is a PNG, so the file you download is far smaller than the uncompressed column; how much smaller depends on the artwork, and the result card shows the real size. If you are looking for an .ico file compressor, the two levers are the same: drop the sizes you do not use (a favicon never needs 256 px), and simplify the artwork, since flat colour and sharp shapes compress much better than photographic detail. Worked example: a favicon with 16, 32 and 48 px frames is 14.7 KB as raw bitmaps, and adding the 256 px frame would bring it to 278.8 KB.

Getting a crisp small icon

Detail that looks fine at 256 px turns to mush at 16 px. Start from a simple, bold mark — a letter, a single shape, strong contrast — and keep thin lines out of it. Artwork that fills the square edge to edge reads better at tiny sizes than a logo with lots of empty padding around it.

Building a modern site? Browsers also want PNG icons and an Apple touch icon — the favicon generator makes that set, and the favicon sizes guide explains which tags to add. Need a single exact size instead? Use the image resizer.