57*57    (iPhone, <=iOS 6.1, standard resolution)
114*114  (iPhone, <=iOS 6.1, high resolution)

60*60    (iPhone, >=iOS 7.0, standard resolution)
120*120  (iPhone, >=iOS 7.0, high resolution)

72*72    (iPad,   <=iOS 6.1, standard resolution)
144*144  (iPad,   <=iOS 6.1, high resolution)

76*76    (iPad,   >=iOS 7.0, standard resolution)
152*152  (iPad,   >=iOS 7.0, high resolution)

512*512    (standard resolution)
1024*1024  (high resolution)

320*480   (3.5 inch, standard resolution)
640*960   (3.5 inch, high resolution)
640*1136  (4.0 inch, high resolution)