...
var ScreenDPI:integer;

implementation
...

      Font.FontHeight := _prop_Font.Size * ScreenDPI div -72;

...

     Control.Font.FontHeight := Size * ScreenDPI div -72;

...


procedure InitScreenDPI;
var dc:THandle;
begin
  dc := GetDC(0);
  ScreenDPI := GetDeviceCaps(dc,LOGPIXELSY);
  ReleaseDC(0,dc);
end;

initialization

InitScreenDPI;

       Font.FontHeight := _prop_Font.Size * ScreenDPI div -72;