A window's size (width and height) is given in pixels. A window can have zero width or height. If an application sets a window's width and height to zero, the system sets the size to the default minimum window size. To discover the default minimum window size, an application uses the GetSystemMetrics function with the SM_CXMIN and SM_CYMIN flags.
An application may need to create a window with a client area of a particular size. The AdjustWindowRect and AdjustWindowRectEx functions calculate the required size of a window based on the desired size of the client area. The application can pass the resulting size values to the CreateWindowEx function.
An application can size a window so that it is extremely large; however, it should not size a window so that it is larger than the screen. Before setting a window's size, the application should check the width and height of the screen by using GetSystemMetrics with the SM_CXSCREEN and SM_CYSCREEN flags.