You may need a lot less, I do when I use a larger needle to make the same size item. Say if you make 9 squares instead of 12, that's 3/4 so you'd probably use about .75 of the yardage. Or if the worsted gauge is 4 sts per inch, and you get 3 per inch that's also .75. If you use a 13 or 15 needle you might get 2 or 2½ sts per inch which may only be about 50-60% of the original yardage.
sue- knitting heretic