I build apps all the time and while preparing for our recent webcast, From Napkin to App: Rapidly Prototype and Build for Mobile, I built out an Adobe Illustrator file that has all sizes of icons and background screens for various iOS and Android devices.
I thought I'd share this collection of pre-sized artboards to use as a template for designing app icons and launch images. It will hopefully save you some time for the tedious task of sizing all your icons and launch images for various mobile devices.
Included are templates for all iOS devices including all iPhone and iPad models current to this posting, plus a reasonable default for Android.
These templates specifically map back to the Android and iOS icon and launch image requirements of trigger.io. I find this a useful tool in my app building toolkit - I hope you will too.