What is an ICO file?
An ICO file is a container format used for Windows icons and browser favicons. Unlike a regular image file, a single .ico can bundle multiple resolutions — so the operating system or browser can pick the sharpest version for wherever the icon appears.
Why inspect an ICO file?
If your favicon looks blurry in certain browsers or disappears entirely in Windows Explorer, it often means a critical size is missing. This viewer shows you exactly which sizes are packed inside the file so you can spot gaps before publishing.
Common ICO sizes and where they're used
- 16×16 — browser tab favicon, taskbar small view
- 32×32 — browser bookmark bar, desktop shortcut
- 48×48 — Windows taskbar pinned icon
- 256×256 — Windows Explorer large icon view, high-DPI displays
PNG vs BMP entries in ICO
Modern tools (including Windows Vista and later) store each size as a compressed PNG inside the ICO container. Older ICO files use raw BMP (device-independent bitmap) data instead. Both formats are valid — but PNG entries produce smaller file sizes and support full alpha transparency.