比例

2x = @2x
Retina 4 = 568h@2x
Retina HD 4.7 = @2x
Retina HD 5.5 = @3x

iOS图标

iPhone 6 Plus              @3x   180 x 180   
iPhone 6 && 5             @2x   120 x 120   
iPhone 4s                    @2x  120 x 120    
iPad && mini2+           @2x   152 x 152   
iPad 2 and iPad mini    @1x   76 x 76

iOS载入图

iOS 7,8 (portrait )  2x              = 640 x 960   
iOS 7,8 (portrait )  Retina 4     = 640 x 1136   
Retina HD 4.7 (portrait)          = 750 x 1334   
Retina HD 5.5 (portrait)          = 1242 x 2208
Retina HD 5.5 (landscape)       = 2208 x 1242

Apple – iOS Human Interface Guidelines

[iOS开发]图标及载入图尺寸