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.
What opens 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
Open a .icns file step by step
- Confirm the file really is a .icns. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with IcoFX or online ICNS converters.
- On Mac, use Preview or Finder (view).
- On Linux, try GIMP (with plugin) or png2icns.
- Still stuck? Convert the .icns to PNG, which opens more widely.
Why can't I open my .icns file?
Almost always because no installed app understands ICNS. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .icns at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
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
What is the .icns file signature (magic bytes)?
A .icns file starts with the hex bytes 69 63 6E 73, which read as icns in ASCII. Programs identify ICNS by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for ICNS. For a full breakdown, see the ICNS file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 69 63 6E 73 | 0 | icns | '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
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