[iOS] Retina display

iPhone and iPod touch

Portrait: 320 x 480 pixels

Portrait Retina: 640 x 960 pixels (@2x)

iPhone 5 and iPod touch (5th generation)

Portrait: 640 x 1136 pixels (@2x)

iPad

Portrait: 768 x 1004 pixels

Portrait Retina: 1536 x 2008 pixels (@2x)

Landscape: 1024 x 748 pixels

Landscape Retina: 2048 x 1496 pixels (@2x)

2048x1536 with 264 ppi.
960x640 with 326 ppi.

normal: 32x32 :image.png
retina: 64x64: image@2x.png

App-Related resources
Font size for Retina display
How to Define UIImageView size as UIImage resolution?
Preparing your iPhone App for Higher Resolution
Detect Retina device
How to serve high-resolution website images for retina displays