What Is Favicon Size?
Favicon Size: The optimal size for creating a favicon is 16×16 pixels, which is the size in which they are most commonly displayed. However, they can sometimes appear in larger dimensions too (such as 32×32 pixels).
A (mostly) complete list of all the known Favorite Icon Sizes
Below is a compiled list of the current known favorite icon sizes, this list is based on the Favorite Icon Cheat Sheet. The greyed out are once legacy favicons, that can still be used but are no longer supported. Due to age, these have been eliminated from the favicons project.
Additional Favicon Sizes:
Purpose: Standard for most desktop browsers
Purpose: Chrome Web Store icon & Small Windows 8 Star Screen Icon*
Purpose: iPad touch icon (Change for iOS 7: up from 144×144)
Purpose: iPad Retina touch icon (change for iOS 10: up from 152×152, not in action. iOS 10 will use 152×152)
Purpose: iPhone Retina
Purpose: Google Developer Web App Manifest Recommendation
Purpose: Chrome for Android home screen icon
Purpose: Standard iOS home screen (iPod Touch, iPhone first generation to 3G)
Purpose: iPad home screen icon
Purpose: GoogleTV icon
Purpose: iPhone retina touch icon (Change for iOS 7: up from 114×114)
Purpose: IE10 Metro tile for pinned site*
Purpose: Opera Speed Dial icon
Purpose: Opera Coast icon