借用Samrat Mazumdar的回答，这里有一个估算设备屏幕大小的简单方法。它适用于最新的设备，但在未来的设备上可能会失败(正如所有猜测的方法一样)。如果设备正在镜像，它也会混淆(返回设备的屏幕大小，而不是镜像的屏幕大小)

#define SCREEN_SIZE_IPHONE_CLASSIC 3.5
#define SCREEN_SIZE_IPHONE_TALL 4.0
#define SCREEN_SIZE_IPAD_CLASSIC 9.7

+ (CGFloat)screenPhysicalSize
{
    if(UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone)
    {
        CGSize result = [[UIScreen mainScreen] bounds].size;
        if (result.height < 500)
            return SCREEN_SIZE_IPHONE_CLASSIC;  // iPhone 4S / 4th Gen iPod Touch or earlier
        else
            return SCREEN_SIZE_IPHONE_TALL;  // iPhone 5
    }
    else
    {
        return SCREEN_SIZE_IPAD_CLASSIC; // iPad
    }
} 

这里是正确的测试设备，不依赖于方向

- (BOOL)isIPhone5
{
    CGSize size = [[UIScreen mainScreen] bounds].size;
    if (MIN(size.width,size.height) == 320 && MAX(size.width,size.height == 568)) {
        return YES;
    }
    return NO;
}

这是我们的代码，在ios7/ios8上测试通过，适用于iphone4、iphone5、ipad、iphone6、iphone6p，无论在设备上还是模拟器上:

#define IS_IPAD (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)
#define IS_IPHONE (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone) // iPhone and       iPod touch style UI

#define IS_IPHONE_5_IOS7 (IS_IPHONE && [[UIScreen mainScreen] bounds].size.height == 568.0f)
#define IS_IPHONE_6_IOS7 (IS_IPHONE && [[UIScreen mainScreen] bounds].size.height == 667.0f)
#define IS_IPHONE_6P_IOS7 (IS_IPHONE && [[UIScreen mainScreen] bounds].size.height == 736.0f)
#define IS_IPHONE_4_AND_OLDER_IOS7 (IS_IPHONE && [[UIScreen mainScreen] bounds].size.height < 568.0f)

#define IS_IPHONE_5_IOS8 (IS_IPHONE && ([[UIScreen mainScreen] nativeBounds].size.height/[[UIScreen mainScreen] nativeScale]) == 568.0f)
#define IS_IPHONE_6_IOS8 (IS_IPHONE && ([[UIScreen mainScreen] nativeBounds].size.height/[[UIScreen mainScreen] nativeScale]) == 667.0f)
#define IS_IPHONE_6P_IOS8 (IS_IPHONE && ([[UIScreen mainScreen] nativeBounds].size.height/[[UIScreen mainScreen] nativeScale]) == 736.0f)
#define IS_IPHONE_4_AND_OLDER_IOS8 (IS_IPHONE && ([[UIScreen mainScreen] nativeBounds].size.height/[[UIScreen mainScreen] nativeScale]) < 568.0f)

#define IS_IPHONE_5 ( ( [ [ UIScreen mainScreen ] respondsToSelector: @selector( nativeBounds ) ] ) ? IS_IPHONE_5_IOS8 : IS_IPHONE_5_IOS7 )
#define IS_IPHONE_6 ( ( [ [ UIScreen mainScreen ] respondsToSelector: @selector( nativeBounds ) ] ) ? IS_IPHONE_6_IOS8 : IS_IPHONE_6_IOS7 )
#define IS_IPHONE_6P ( ( [ [ UIScreen mainScreen ] respondsToSelector: @selector( nativeBounds ) ] ) ? IS_IPHONE_6P_IOS8 : IS_IPHONE_6P_IOS7 )
#define IS_IPHONE_4_AND_OLDER ( ( [ [ UIScreen mainScreen ] respondsToSelector: @selector( nativeBounds ) ] ) ? IS_IPHONE_4_AND_OLDER_IOS8 : IS_IPHONE_4_AND_OLDER_IOS7 )

通过这种方式，您可以检测设备系列。

    #import <sys/utsname.h>
    NSString* deviceName()
    {
        struct utsname systemInformation;
        uname(&systemInformation);
        NSString *result = [NSString stringWithCString:systemInformation.machine
                                              encoding:NSUTF8StringEncoding];
        return result;
    }

    #define isIPhone5  [deviceName() rangeOfString:@"iPhone5,"].location != NSNotFound
    #define isIPhone5S [deviceName() rangeOfString:@"iPhone6,"].location != NSNotFound

CGFloat height = [UIScreen mainScreen].bounds.size.height;

NSLog(@"screen soze is %f",height);

  if (height>550) {

          // 4" screen-do some thing
     }

  else if (height<500) {

        // 3.5 " screen- do some thing

     }

我发现答案并不包括模拟器的特殊情况。

#define IS_WIDESCREEN ( [ [ UIScreen mainScreen ] bounds ].size.height == 568  )
#define IS_IPHONE ([[ [ UIDevice currentDevice ] model ] rangeOfString:@"iPhone"].location != NSNotFound)
#define IS_IPAD ([[ [ UIDevice currentDevice ] model ] rangeOfString:@"iPad"].location != NSNotFound)
#define IS_IPHONE_5 ( IS_IPHONE && IS_WIDESCREEN )