ICO is still the format Windows Explorer, older browsers, and desktop apps expect for icons. This converter takes a PNG source (ideally 256×256 or larger, square) and produces a multi-size ICO with sizes chosen from a checklist. Downscaling uses high-quality Lanczos filtering to keep small sizes crisp.
Multi-size vs. single-size ICO
A single-size ICO (say, 32×32 only) gets scaled by Windows to fit other contexts, which looks blurry. A multi-size ICO includes rasters at each target size so Windows can pick a pixel-perfect match — 16 for the tab, 48 for the taskbar, 256 for Explorer's icon view. Always ship multi-size unless size is a hard constraint.
Source resolution matters
Start with the highest-resolution PNG you have — ideally 256×256 or 512×512. The tool downscales to smaller sizes with Lanczos filtering, which preserves sharpness better than nearest-neighbor. Never upscale — a 32×32 source rendered at 128 will look blurry no matter the filter.
Beyond favicon
ICO isn't just for browsers — desktop apps (Windows Explorer, taskbar, Start menu tile) all use ICO. If you're shipping an Electron or .NET app, the ICO output here goes straight into your build config. NSIS, Inno Setup, and WiX all accept these files directly.