in iPhone App How to detect the screen resolution of the device

In iPhone App, while running the App on device How to detect the screen resolution of the device on which App is running?

CGRect screenBounds = [[UIScreen mainScreen] bounds];

That will give you the entire screen's resolution in points, so it would most typically be 320x480 for iPhones. Even though the iPhone4 has a much larger screen size iOS still gives back 320x480 instead of 640x960. This is mostly because of older applications breaking.

CGFloat screenScale = [[UIScreen mainScreen] scale];

This will give you the scale of the screen. For all devices that do not have Retina Displays this will return a 1.0f, while Retina Display devices will give a 2.0f and the iPhone 6 Plus (Retina HD) will give a 3.0f.

Now if you want to get the pixel width & height of the iOS device screen you just need to do one simple thing.

CGSize screenSize = CGSizeMake(screenBounds.size.width * screenScale, screenBounds.size.height * screenScale);

By multiplying by the screen's scale you get the actual pixel resolution.

A good read on the difference between points and pixels in iOS can be read here.

EDIT: (Version for Swift)

let screenBounds = UIScreen.main.bounds
let screenScale = UIScreen.main.scale
let screenSize = CGSize(width: screenBounds.size.width * screenScale, height: screenBounds.size.height * screenScale)

UIScreen class lets you find screen resolution in Points and Pixels.

Screen resolutions is measured in Points or Pixels. It should never be confused with screen size. A smaller screen size can have higher resolution.

UIScreen's 'bounds.width' return rectangular size in Points

UIScreen's 'nativeBounds.width' return rectangular size in Pixels.This value is detected as PPI ( Point per inch ). Shows the sharpness & clarity of the Image on a device.

You can use UIScreen class to detect all these values.

Swift3

// Normal Screen Bounds - Detect Screen size in Points.
let width = UIScreen.main.bounds.width
let height = UIScreen.main.bounds.height
print("\n width:\(width) \n height:\(height)")

// Native Bounds - Detect Screen size in Pixels.
let nWidth = UIScreen.main.nativeBounds.width
let nHeight = UIScreen.main.nativeBounds.height
print("\n Native Width:\(nWidth) \n Native Height:\(nHeight)")

Console

width:736.0 
height:414.0

Native Width:1080.0 
Native Height:1920.0

Swift 2.x

//Normal Bounds - Detect Screen size in Points.
    let width  = UIScreen.mainScreen.bounds.width
    let height = UIScreen.mainScreen.bounds.height
                    
// Native Bounds - Detect Screen size in Pixels.
    let nWidth  = UIScreen.mainScreen.nativeBounds.width
    let nHeight = UIScreen.mainScreen.nativeBounds.height

ObjectiveC

// Normal Bounds - Detect Screen size in Points.
CGFloat *width  = [UIScreen mainScreen].bounds.size.width;
CGFloat *height = [UIScreen mainScreen].bounds.size.height;

// Native Bounds - Detect Screen size in Pixels.
CGFloat *width  = [UIScreen mainScreen].nativeBounds.size.width
CGFloat *height = [UIScreen mainScreen].nativeBounds.size.width

Use it in App Delegate: I am using storyboard

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{

if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone) {
    
    CGSize iOSDeviceScreenSize = [[UIScreen mainScreen] bounds].size;
    
    //----------------HERE WE SETUP FOR IPHONE 4/4s/iPod----------------------
    
    if(iOSDeviceScreenSize.height == 480){          
        
        UIStoryboard *iPhone35Storyboard = [UIStoryboard storyboardWithName:@"iPhone" bundle:nil];
        
        // Instantiate the initial view controller object from the storyboard
        UIViewController *initialViewController = [iPhone35Storyboard instantiateInitialViewController];
        
        // Instantiate a UIWindow object and initialize it with the screen size of the iOS device
        self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
        
        // Set the initial view controller to be the root view controller of the window object
        self.window.rootViewController  = initialViewController;
        
        // Set the window object to be the key window and show it
        [self.window makeKeyAndVisible];
        
        iphone=@"4";
        
        NSLog(@"iPhone 4: %f", iOSDeviceScreenSize.height);
      
    }
    
    //----------------HERE WE SETUP FOR IPHONE 5----------------------
    
    if(iOSDeviceScreenSize.height == 568){
        
        // Instantiate a new storyboard object using the storyboard file named Storyboard_iPhone4
        UIStoryboard *iPhone4Storyboard = [UIStoryboard storyboardWithName:@"iPhone5" bundle:nil];
        
        // Instantiate the initial view controller object from the storyboard
        UIViewController *initialViewController = [iPhone4Storyboard instantiateInitialViewController];
        
        // Instantiate a UIWindow object and initialize it with the screen size of the iOS device
        self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
        
        // Set the initial view controller to be the root view controller of the window object
        self.window.rootViewController  = initialViewController;
        
        // Set the window object to be the key window and show it
        [self.window makeKeyAndVisible];
        
         NSLog(@"iPhone 5: %f", iOSDeviceScreenSize.height);
        iphone=@"5";
    }
       
} else if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
    // NSLog(@"wqweqe");
    storyboard = [UIStoryboard storyboardWithName:@"iPad" bundle:nil];
    
}

 return YES;
 }

For iOS 8 we can just use this [UIScreen mainScreen].nativeBounds , like that:

- (NSInteger)resolutionX
{
    return CGRectGetWidth([UIScreen mainScreen].nativeBounds);
}

- (NSInteger)resolutionY
{
    return CGRectGetHeight([UIScreen mainScreen].nativeBounds);
}

See the UIScreen Reference: http://developer.apple.com/library/ios/#documentation/uikit/reference/UIScreen_Class/Reference/UIScreen.html

if([[UIScreen mainScreen] respondsToSelector:NSSelectorFromString(@"scale")])
{
	if ([[UIScreen mainScreen] scale] < 1.1)
		NSLog(@"Standard Resolution Device");

	if ([[UIScreen mainScreen] scale] > 1.9)
		NSLog(@"High Resolution Device");
}

Use this code it will help for getting any type of device's screen resolution

 [[UIScreen mainScreen] bounds].size.height
 [[UIScreen mainScreen] bounds].size.width

If your goal is to get the model resolution type and not the resolution values themeselfs, this Swift solution might be helpful:

import UIKit

@objc(IphoneModelScreenSize)
public class IphoneModelScreenSize: NSObject {

    // MARK: Enums

    public enum IphoneModelScreenSize: Int {
    case notAnIphone = 0,
         twoThreeOrFour = 1,
         se = 2,
         sixSevenOrEight = 3,
         plus = 4,
         elevenXorXS = 5,
         elevenProMaxOrXsMax = 6
    }

    // MARK: Class properties

    public class func screenSize() -> IphoneModelScreenSize {
        let bounds = UIScreen.main.bounds
        let screenWidth = bounds.size.width
        let screenHeight = bounds.size.height

        switch (screenWidth, screenHeight) {
        case (320.0, 480.0):
          return .twoThreeOrFour
        case (320.0, 568.0):
          return .se
        case (375.0, 667.0):
          return .sixSevenOrEight
        case (414.0, 736.0):
          return .plus
        case (375.0, 812.0):
          return .elevenXorXS
        case (414.0, 896.0):
          return .elevenProMaxOrXsMax
        default:
          return .notAnIphone
        }
    }

    public class func screenSizeStringValue() -> String {
        return screenSizeEnumToString(screenSize())
    }

    // MARK: Private properties

    private class func screenSizeEnumToString(_ screenSize: IphoneModelScreenSize) -> String {
        var screenSizeAsString: String

        switch screenSize {
        case .notAnIphone:
            screenSizeAsString = "Not an Iphone"
        case .twoThreeOrFour:
            screenSizeAsString = "2G, 3G, 3GS, 4 or 4s"
        case .se:
            screenSizeAsString = "5, 5s, 5c or SE"
        case .sixSevenOrEight:
            screenSizeAsString = "6, 6s, 7 or 8"
        case .plus:
            screenSizeAsString = "6+, 6s+, 7+ or 8+"
        case .elevenXorXS:
            screenSizeAsString = "11 Pro, X or Xs"
        case .elevenProMaxOrXsMax:
            screenSizeAsString = "11, Xr, 11 Pro Max or Xs Max"
        }

        return screenSizeAsString
    }

}