Icon and Image Sizes

https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/IconMatrix.html#//apple_ref/doc/uid/TP40006556-CH27-SW1

Icon and Image Sizes

Every app needs an app icon and a launch file or image. In addition, some apps need custom icons to represent app-specific content, functions, or modes in navigation bars, toolbars, and tab bars.

Unlike other custom artwork in your app, the icons and images listed in Table 41-1 must meet specific criteria so that iOS can display them properly. In addition, some icon and image files have naming requirements (to learn about naming these files, see App Icons and App Launch (Default) Images).

Table 41-1Size (in pixels) of custom icons and images

Asset	iPhone 6 Plus (@3x)	iPhone 6 and iPhone 5 (@2x)	iPhone 4s (@2x)	iPad and iPad mini (@2x)	iPad 2 and iPad mini (@1x)
App icon (required for all apps)	180 x 180	120 x 120	120 x 120	152 x 152	76 x 76
App icon for the App Store (required for all apps)	1024 x 1024	1024 x 1024	1024 x 1024	1024 x 1024	1024 x 1024
Launch file or image (required for all apps)	Use a launch file (see Launch Images)	For iPhone 6, use a launch file (see Launch Images) For iPhone 5, 640 x 1136	640 x 960	1536 x 2048 (portrait) 2048 x 1536 (landscape)	768 x 1024 (portrait) 1024 x 768 (landscape)
Spotlight search results icon (recommended)	120 x 120	80 x 80	80 x 80	80 x 80	40 x 40
Settings icon (recommended)	87 x 87	58 x 58	58 x 58	58 x 58	29 x 29
Toolbar and navigation bar icon (optional)	About 66 x 66	About 44 x 44	About 44 x 44	About 44 x 44	About 22 x 22
Tab bar icon (optional)	About 75 x 75 (maximum: 144 x 96)	About 50 x 50 (maximum: 96 x 64)	About 50 x 50 (maximum: 96 x 64)	About 50 x 50 (maximum: 96 x 64)	About 25 x 25 (maximum: 48 x 32)
Default Newsstand cover icon for the App Store (required for Newsstand apps)	At least 1024 pixels on the longest edge	At least 1024 pixels on the longest edge	At least 1024 pixels on the longest edge	At least 1024 pixels on the longest edge	At least 512 pixels on the longest edge
Web clip icon (recommended for web apps and websites)	180 x 180	120 x 120	120 x 120	152 x 152	76 x 76

For all images and icons, the PNG format is recommended. You should avoid using interlaced PNGs.

The standard bit depth for icons and images is 24 bits—that is, 8 bits each for red, green, and blue—plus an 8-bit alpha channel, for a total of 32 bits.

You don’t need to constrain your palette to web-safe colors.