ICNS (Mac icon)
Also known as: .icns file, Apple icon image, Mac app icon
ICNS is Apple’s icon format that bundles many sizes and resolutions of a single app icon into one file, so macOS can show it crisply everywhere from the Dock to a Finder list. It is the Mac counterpart to Windows’ ICO format.
- Apple’s icon format for macOS apps
- Bundles many icon sizes in one file
- The Mac counterpart to Windows’ ICO format
Why an icon needs many sizes
macOS displays the same app icon at very different sizes — tiny in a list, large in the Dock, full size in Get Info. Rather than rescale one image and risk blurriness, an ICNS file packs multiple pre-made bitmaps, from small to high-resolution Retina, into one container.
This is the same problem ICO solves on Windows: one file, many embedded sizes, so the system always has a sharp version on hand.
Creating ICNS files
App developers generate an ICNS from a high-resolution master image — usually a PNG — exported at each required size. macOS then chooses the right size automatically depending on where the icon appears.
Because it holds several bitmaps, an ICNS file is larger than any single PNG inside it, but it is still small overall and lives with the app rather than in your photo library.