Image Format Comparison

ICNS vs ICO — macOS Icons vs Windows Icons

ICNS is Apple's icon format used by macOS applications and system icons. ICO is Microsoft's icon format. Both bundle multiple resolutions in a single file and support transparency, but the binary structures are completely different. Cross-platform applications need both formats — one for each operating system.

ICNSvsICO

Quick Verdict

Use ICNS when…

Use ICNS for macOS apps. Required by Xcode for app bundles, used by Finder for custom folder icons, and by macOS for any iconic representation.

Use ICO when…

Use ICO for Windows apps and websites. Required for Windows .exe icon embedding, favicon.ico (web), and any Windows iconography.

ICNS vs ICO: Feature Comparison

Feature	ICNS	ICO
Operating system	macOS	Windows
Maximum resolution	1024×1024	256×256 (standard)
Multi-resolution	Yes	Yes
Transparency	Full alpha	Full alpha
Compression	PNG-based (modern ICNS)	PNG or BMP
Web favicon use	No	Yes (favicon.ico)

When ICNS wins

✓Operating system: macOS
✓Maximum resolution: 1024×1024
✓Multi-resolution: Yes

When ICO wins

✓Operating system: Windows
✓Maximum resolution: 256×256 (standard)
✓Multi-resolution: Yes

Frequently asked questions

How do I convert ICNS to ICO?

Use ImageMagick: `convert input.icns -resize 256x256 output.ico`. Or extract the largest size from ICNS (`iconutil -c iconset input.icns`) then build an ICO with multiple sizes. macOS-only: `sips -s format png input.icns --out output.png`.

Can I use a single icon for both macOS and Windows apps?

No — you need both an ICNS for macOS and an ICO for Windows. Build tools like Electron Builder accept both formats automatically. Provide source PNGs at 16, 32, 48, 64, 128, 256, 512, and 1024 pixels and the build pipeline generates both icon files.