What is the ICON file format?
.icon is a non-standardized extension used by various icon editors and applications to save small bitmap images intended as program or UI icons. No single organization owns the format and no universal binary specification exists; files may internally be .ico (Windows Icon format), .png, BMP, or an application-specific binary.
When the internal format is ICO-compatible - the most common case - the file begins with the 4-byte header 00 00 01 00, followed by an ICONDIRENTRY array describing each embedded image size, and then the image data blocks (DIB bitmap or embedded PNG). A single ICO-based .icon file can bundle multiple resolutions - typically 16×16, 32×32, 48×48, 64×64, 128×128, and 256×256 pixels - so the OS or application selects the most appropriate size at runtime.
On Windows, .ico is the native standard; .icon is a non-standard alias that some editors use. On macOS, the native icon format is .icns (Apple Icon Image format), not .icon. If an application does not recognize a .icon file, renaming it to .ico usually resolves the issue for ICO-based files.
Applications such as IconoMaker, Perfect Icon, Axialis IconWorkshop, GIMP, and Adobe Photoshop can open and save .icon files; IrfanView and XnView display them when the internal format is ICO or PNG.
Security & safety
RISK: LOW.icon files are passive image data. No executable code; no known exploits in well-maintained image editors. Rename to .ico and open in any image viewer safely.
Format details
in a nutshell- macOS Finder Icon (custom folder/file icon) - macOS stores custom icons in the resource fork or as a hidden .icon file in some contexts; these are ICNS-compatible, not Windows ICO.
- Application-specific icon package files - Some icon editors (Axialis IconWorkshop, others) may use .icon as a project/export extension.
Programs that open ICON files
Windows10 apps
IconoMaker
Free Free icon editor; creates ICO-compatible .icon files. Verify website is current before recommending. 
Adobe Photoshop
Paid Opens ICO-format .icon files (may need to rename to .ico first). Save As ICO requires the free ICO plugin. 
GIMP
Open-source File > Open - GIMP opens ICO-format .icon files and lets you edit each size layer. Free. 
FastPictureViewer Professional
Paid Windows Explorer codec for fast preview of icon/ICO images; paid. 
Axialis IconWorkshop
Paid Professional icon editor; open, edit, and export .icon files. Creates multi-size ICO packages. 
macOS2 apps
Linux1 app
Technical details
deep spec| Internal format | Typically Windows ICO (`00 00 01 00` header); may also be PNG, BMP, or application-specific binary |
| ICO magic bytes | `00 00 01 00` at offset 0 (when ICO-based) |
| Byte order | Little-endian (ICO / BMP-based files) |
| Colour depth | 1 bpp, 4 bpp, 8 bpp, 24 bpp, or 32 bpp (32 bpp includes 8-bit alpha channel) |
| Supported frame sizes | 16×16 to 256×256 px per frame (ICO standard); some editors support 512×512 and larger |
| Multi-size container | ICO `ICONDIR` supports up to 255 image frames per file |
| Compression | None for BMP-based frames; DEFLATE for PNG-embedded frames (supported since Windows Vista) |
| Transparency | 1-bit XOR mask (legacy ICO) or 8-bit alpha channel (32 bpp ICO / PNG frames) |
| Typical file size | 1 KB - 500 KB |
| Standardization | Non-standard alias for `.ico` in most contexts; no registered format specification or MIME type |
| macOS distinction | `.icns` is the native macOS icon format; `.icon` on macOS is not an alias for `.icns` |
| MIME type | `image/x-icon` (inherited from ICO; not formally registered for the `.icon` extension) |
| Released | N/A (extension used by multiple unrelated tools) |
ICON conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about ICON files.
