General

• 16x16: browser favicon
• 32x32: taskbar shortcut icon
• 96x96: desktop shortcut icon (and Google TV)
• 152×152: iPad touch icon (Change for iOS 7: up from 144×144)
• 167×167: iPad Retina touch icon (change for iOS 10: up from 152×152, not in action. iOS 10 will use 152×152)
• 180×180: iPhone Retina
• 128x128: Chrome Webstore icon
• 196x196: Android Chrome icon
• 228x228: Opera Coast icon

Reference

• IE 9
• IE11
Microsoft Edge
• Chrome
• IOS