How to get scale ratio between design window size (in VS forms designer) and real size?

  c++, dialog, size, winapi, window-resize

I have a standard WinApi Dialog window, created in form designer of Visual Studio. Design size is eg. 500×600 in pixels. But if I run application and get size of window (GetWindowSize()), the size is different, almost bigger, dependent of the monitor resolution.

According to this ratio I must adjust also font size, and child window possition and size…
Where I get this ratio?

Thank for help.

Source: Windows Questions C++