If the material is 1.2 wide i would probably go for 3 widths per side especially if it is a lightish weight fabric....it will give a more lush finish. By the time you take all the seams into account 2 widths per side is only just going to get there. They say an absolute minimum of 2.5 times the width for gathering and 3 times the width for lush gathers. Also dont forget the curtains may need to be wider than the window width as the curtain track, if done correctly will actually sit wider than the width of the window to allow the curtains to pull back exposing as much of the window light as possible, if that makes sense. For example our tracks are 40cms wider each side of the window on our 1.8m windows to allow for curtain pullback. hope that heps Kate.