The UIDevice class can help us do that like so:
[super viewDidLoad];
// lets detect the height of our screen here
int height = [UIScreen mainScreen].bounds.size.height;
int width = [UIScreen mainScreen].bounds.size.width;
// share the news
NSString *message = [[NSString alloc]initWithFormat:@"This screen is \n\n%i pixels high and\n%i pixels wide", height, width];
NSLog(@"%@", message);
This will work fine in your View Controllers and App Delegate files.
I’ve got a full working demo project on GitHub: https://github.com/versluis/ScreenSize
Further Reading: