Two ways to make an ICO from PNG files
One ICO from each PNG
This is the default. Each PNG that you add becomes its own .ico file, with the sizes that you ticked. The sizes are drawn from your picture one by one, so the small ones are sharp. Transparency stays transparent.
Combine several PNGs into one ICO
If you drew the icon yourself at 16, 32 and 48 pixels, or got separate files from a designer, choose Combine all PNG files into one ICO. Every PNG becomes one image inside the ICO, at the size that it already has. A square PNG of 256 pixels or less is copied into the ICO exactly as it is, without any change of its pixels. A bigger or non-square one is fitted into a 256 pixel square.
What size should the PNG be?
Start from a square PNG of at least 256 by 256 pixels. A source that is smaller than the biggest size that you ask for has to be enlarged, and the result looks soft, so the tool warns you. A PNG that is not square is fitted inside a square, with transparent bars at the sides.
Which sizes to put in the ICO
- 16 and 32 pixels for browser tabs and bookmarks.
- 48 pixels for Windows shortcuts and some search results.
- 64, 128 and 256 pixels for large Windows icons. Add them for application icons, and leave them out for favicons to keep the file small.
Transparency
PNG supports transparency, and so does ICO. The transparent parts of your image stay transparent. If you would rather have a solid background, choose a color, and you can also round the corners or cut a circle.
How the ICO is stored
Each size is stored inside the ICO as a PNG image. This is the modern form of the format. It keeps the files small and the colors exact, and every current browser and Windows since Vista can read it. Everything is done in your browser and your files are not uploaded.
For a JPG, use JPG to ICO, which can also remove a white background. To convert both ways, use the ICO converter, and for a full website icon set, see favicon from image.