What is a .icns file?
Apple Icon Image · Image · Apple · 2000s
ICNS is the Mac equivalent of an ICO: a single file bundling one app or folder icon at every size macOS needs, from a small toolbar icon up to a huge Retina-resolution image. You meet it inside Mac app packages far more often than as a standalone download.
What is a .icns file used for?
An ICNS file is a short header followed by a sequence of typed icon entries, each a specific pixel size, from 16x16 up to 1024x1024 for Retina displays, so macOS always has a crisp size ready to show.
Modern icon entries inside the file are compressed as PNG or JPEG 2000 data rather than stored as raw bitmaps, keeping the overall file reasonably small despite holding many sizes.
You mostly meet an ICNS bundled inside a Mac app package, at Contents/Resources/AppIcon.icns, rather than as something you download on its own, which is why dedicated ICNS tools, rather than everyday photo apps, are what create and edit one directly.
To make your own, start from a square image at 1024x1024 and run it through an icon-conversion tool, the same way a favicon ICO is built from a square PNG.
How to open a .icns file
The .icns format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- IcoFX
- online ICNS converters
macOS
- Preview
- Finder (view)
- Icon Composer (legacy)
Linux
- GIMP (with plugin)
- png2icns
Web
- Online ICNS converters
How to convert a .icns file
You can convert a .icns file to PNG, ICO using a conversion tool or the export menu of an app that opens it.
Convert images free: ImageConvert
.icns file signature (magic bytes)
Programs recognise a .icns file by the bytes at the start of the file, not by its name. These are the signatures for ICNS. For a full breakdown, see the ICNS file signature page.
| Hex signature | Offset | Note |
|---|---|---|
| 69 63 6E 73 | 0 | 'icns' |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .icns file?
ICNS is the Mac equivalent of an ICO: a single file bundling one app or folder icon at every size macOS needs, from a small toolbar icon up to a huge Retina-resolution image. You meet it inside Mac app packages far more often than as a standalone download.
How do I open an ICNS file on Windows?
Windows has no built-in viewer for ICNS. Use a converter such as IcoFX or an online ICNS-to-PNG converter to view or reuse the icon.
How do I make an ICNS icon?
Start with a square image, ideally 1024x1024, and run it through an icon tool that packs the required sizes into one .icns file. macOS developer tools and several free online converters both do this.
Related formats
Sources
Details on this page were checked against authoritative references: