This tool will produce a zip file containing the following sizes (and purpose):
SizePurpose
1024x1024 iTunes Connect App Store Icon 1024
226x226 iTunes Connect App Store Icon 226
88x88 iTunes Connect App Store Icon 88
180x180 XCode iPhone App 60pt 3x 180
120x120 XCode iPhone Spotlight 40pt 3x 120
512x512 XCode iPhone Launch Screen 512
40x40 XCode iPhone Notification 20pt 2x 40
60x60 XCode iPhone Notification 20pt 3x 40
80x80 XCode iPhone Spotlight 40pt 2x 80
87x87 XCode iPhone Settings 29pt 3x 87
58x58 XCode iPhone Settings 29pt 2x 58
76x76 XCode iPad App 76pt 1x 76
152x152 XCode iPad App 76pt 2x 152
167x167 XCode iPad Pro App 83.5 2x 167
20x20 XCode iPad Notification 20pt 1x 20
40x40 XCode iPad Notification 20pt 2x 40
40x40 XCode iPad Spotlight 40pt 1x 40
80x80 XCode iPad Spotlight 40pt 2x 80
29x29 XCode iPad Settings 29pt 1x 29
58x58 XCode iPad Settings 29pt 2x 58
87x87 XCode WatchKit Companion Settings 29pt 3x 87
58x58 XCode WatchKit Companion Settings 29pt 2x 58
172x172 XCode WatchKit Short Look 86pt 2x 172
196x196 XCode WatchKit Short Look 98pt 2x 196
55x55 XCode WatchKit Notification Center 27.5pt 2x 55
48x48 XCode WatchKit Notification Center 24pt 2x 48
203x203 XCode WatchKit Ext Extra Large Simple Comp 42mm 101.5 2x 203
182x182 XCode WatchKit Ext Extra Large Simple Comp 38mm 91 2x 182
58x58 XCode WatchKit Ext Modular Simple Comp 42mm 29 2x 58
52x52 XCode WatchKit Ext Modular Simple Comp 38mm 26 2x 52
44x44 XCode WatchKit Ext Utilitarian Simple Comp 42mm 22 2x 44
40x40 XCode WatchKit Ext Utilitarian Simple Comp 38mm 20 2x 40
36x36 XCode WatchKit Ext Circular Simple Comp 42mm 18 2x 36
32x32 XCode WatchKit Ext Circular Simple Comp 38mm 16 2x 32
Upload a square PNG image here (minimum 2048x2048, maximum 4096x4096):