Use GetSystemMetrics WinAPI function with SM_CYHSCROLL and SM_CXVSCROLL parameters.
procedure TForm1.Button1Click(Sender: TObject); begin Label1.Caption:='Height of a horizontal scroll bar = '+ IntToStr(GetSystemMetrics(SM_CYHSCROLL))+' pixels'; Label2.Caption:='Width of a vertical scroll bar = '+ IntToStr(GetSystemMetrics(SM_CXVSCROLL))+' pixels'; end;