Question 1

What is a 256×256 ICO used for?

Accepted Answer

Windows application icons at the largest display size (Extra Large Icons view in Explorer), high-DPI displays, and Windows Store/installer icons. Also used for macOS dock icons (inside .icns files).

Question 2

Can I use this for a macOS app icon?

Accepted Answer

macOS uses .icns format, not .ico. However, the 256×256 size is standard for both platforms. Convert with iconutil (macOS) or png2icns. macOS app icons should include sizes up to 1024×1024.

Sample App Icon — 256×256 ICO

Other ICO files

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