GUI Label Width & Height

I'm having trouble with this, I'm not that familiar with the GUI yet. Basically, I want to have the Width and Height of my label equals the size of the font, if that makes sense?

  GUI.Label(new Rect(Screen.width/2 - x1/2,  Screen.height/2 - y1/2,w1, h1),"Hello", style1);

I want it so that when I click it, it'll do something but without a width and height equal to the label/font size, you can't click it as it is 0.