Problem in setting GUI Button for mobile device

I want to position my gui button to bottom right corner of mobile devices.

But i am not getting the way to position my button which applies to all my devices with different resolution.

If you guys have any idea , then please help me.

THanks for your support and help in advance.

Usually I will use code like the following:

void OnGUI
  int buttonWidth = Screen.width * 0.1f;
  int buttonHeight = Screen.height * 0.1f;

  if (GUI.Button (new Rect (Screen.width - buttonWidth, Screen.height - buttonHeight, buttonWidth, buttonHeight), "button text"))
    // do button stuff here

Obviously there are things you can do to optimize so you are not doing the calculation every OnGUI, but only if you know the screen size is not going to change or you handle a screen size change event and do the calculations there.