PNG to ICO Converter

An ICO file is a small container that holds the same icon at several sizes, so Windows can pick a crisp 16 px version for a list view and a 256 px one for large desktop icons. This converter draws your PNG at each size you tick, high-quality downscaling in steps, and writes a real multi-image .ico — not a renamed PNG. Everything runs in your browser; your images never leave your device.

How to use this tool

1. Choose a PNG — ideally square, 256 × 256 px or larger, with a transparent background.
2. Tick the sizes to include (16, 32, 48 and 256 cover Windows Explorer, the taskbar and shortcuts).
3. Pick how a non-square picture is fitted: padded, cropped or stretched.
4. Download the .ico and check the list of sizes inside it.

Formula

ICO = ICONDIR (6 bytes: 0, type 1, count) + one 16-byte ICONDIRENTRY per image (width, height — 0 means 256 — colour count 0, planes 1, 32 bits per pixel, byte length, offset) + the image data.

Each image is stored as a PNG, which Windows Vista and later read directly. The classic option stores 48 px and smaller sizes as 32-bit BMP data instead (a 40-byte header with the height doubled, bottom-up BGRA pixels, then a 1-bit transparency mask), which Windows XP and some older programs need.

Example

With only 16 px ticked and classic entries on, the file is exactly 1,150 bytes: 6 bytes of directory, a 16-byte entry, a 40-byte header, 16 × 16 × 4 = 1,024 bytes of colour and a 64-byte mask (16 rows × 4 bytes). With the default 16/32/48/256 set the four images are PNG-compressed, and a simple logo typically produces an icon of a few tens of kilobytes.