What do you mean by a full size quilt? How big is that?
OBW actually results in practically no fabric waste, but like as Amma pointed out it will use more fabric if you use smaller strips (like all quilts do).
In the first OBW book, Maxine Rosenthal gives an estimate of 4.5 yards for a "lap-size, twin, or full-size" quilt. (I think of those as 3 different sizes, so not sure what she means.) For a queen or larger, she says 9 yards. Both estimates are for hexagon blocks. It takes more for the octagon blocks. And... it also depends on which strip size you use.