What is inside an ICO file
An ICO file is a small container. It starts with a list of the images it holds, followed by the images themselves, one per size, so the program showing the icon can use the size that fits. That is why one PNG becomes several images here: each size is scaled down from your original in steps, so the small ones stay clean instead of blurry.
Microsoft's guidelines name 16, 32, 48 and 256 px as the full set for application icons and add that only the 256 px image should be compressed, to keep the file small. This converter follows that: the 256 px entry is PNG, the others are plain bitmaps. Screens set to a higher scale need more pixels for the same icon, which is where 64 px helps:
| Display scale | Small icon | Large icon |
|---|---|---|
| 100% | 16 × 16 | 32 × 32 |
| 125% | 20 × 20 | 40 × 40 |
| 150% | 24 × 24 | 48 × 48 |
| 200% | 32 × 32 | 64 × 64 |
Scale factors from Microsoft's Windows icon guidelines.
Tips for a clean icon
- Start big and square: a 256 × 256 px PNG or larger gives every size enough pixels to work from. The image cropper makes a square 1:1 crop.
- Keep it simple: at 16 px there are only 256 pixels. Bold shapes and one or two letters read better than a detailed logo.
- Need a full favicon set? The favicon generator adds the PNG sizes, an Apple touch icon, a web manifest and the HTML code. Have a vector logo? Make a large PNG of it with SVG to PNG first.
Making the icon
- 1Tick the sizes the file should hold. 16, 32 and 48 px are on already.
- 2Drop your PNG on the box. Several PNGs give several icon files.
- 3Save the .ico file, rename it to favicon.ico for a website if you like, and use it.
Frequently asked questions
Which sizes should an ICO file contain?
Microsoft's Windows design guidelines list 16x16, 32x32, 48x48 and 256x256 as the full set for an application icon, and note that Windows scales larger sizes down when one is missing. For a website favicon.ico, the default of 16, 32 and 48 px is what our favicon generator uses too.
Is this a real ICO file or a renamed PNG?
A real one. The file starts with an icon directory and holds every size you tick as its own image. Sizes up to 128 px are stored as 32-bit bitmaps with an alpha channel, the classic form that old programs read too. The 256 px image is stored as PNG, which Windows reads inside icons since Windows Vista and which keeps the file small.
Is the transparent background kept?
Yes. Every size keeps the full alpha channel of your PNG, so soft edges and shadows stay smooth. Each bitmap also gets the classic transparency mask for programs that ignore alpha.
What if my image is not square?
An icon is square, so the image is scaled to fit and centered on a transparent square. Nothing is cut off. If you would rather fill the square, crop the PNG to 1:1 with the image cropper first.
Are my images uploaded?
No. The icon file is built by your browser on your own device. Nothing is sent to a server.