Use ClientHeight to determine the height (in pixels) of the form's client area. The client area is the usable area inside the form's border, excluding the title bar, scroll bars, and so on. 

Set ClientHeight to change the height of the form's window based on the desired client area. To change the height of the form's window based on the total size of the window (including the border, menu, status bar and so on), use the Height property instead.  

Delphi Examples: 

{
This example reduces the height of the form's client area by
half when the user clicks the button on the form:
Note that only the client area is halved, not the entire form.
}
procedure TForm1.Button1Click(Sender: TObject);
begin
  ClientHeight := ClientHeight div 2;
end;

ClientRect 

ClientWidth 

Height