Just to re-post this.

• iPhone 3+4 (3.5 Inch)
  • 640 x 960
• iPhone 5 (4 Inch)
  • 640 x 1136
• iPhone 6 (4.7 Inch)
  • 750 x 1334
• iPhone 6 Plus (5.5 Inch)
  • 1242 x 2208
  • the phone scales them down to 1080 x 1920
• iPad (Air and Mini Retina)
  • 1536 x 2048
• Apple Watch
  • 312 x 390 pixels

http://stackoverflow.com/questions/25756589/itunes-connect-screenshots-sizes-for-all-ios-iphone-ipad-apple-watch-devices

http://appstoreoptimization.at/itunes-connect-screenshot-size-iphone-6/