iOS Interface Guidelines

http://developer.apple.com/library/ios/#documentation/userexperience/conceptual/mobilehig/IconsImages/IconsImages.html

http://developer.apple.com/library/ios/#documentation/userexperience/conceptual/mobilehig/TranslateApp/TranslateApp.html#//apple_ref/doc/uid/TP40006556-CH10-SW2

ICON: 
For iPhone and iPod touch both of these sizes are required:

• 57 x 57 pixels
• 114 x 114 pixels (high resolution)

For iPad, both of these sizes are required:

• 72 x 72 pixels
• 144 x 144 (high resolution)

DISPLAY:

For standard iPhone 4 and iPod touch devices:

• 320 x 480 pixels
• 640 x 960 pixels (high resolution)

For apps that run on iPhone 5 and iPod touch (5th generation), 

create a launch image that measures 

• 640 x 1136 pixels.

For iPad launch images, do not include the status bar region. Create launch images of these sizes (most iPad apps should supply a launch image for each orientation):

For portrait:

• 768 x 1004 pixels
• 1536 x 2008 pixels (high resolution)

For landscape:

• 1024 x 748 pixels
• 2048 x 1496 pixels (high resolution)