I've found most scrappy patterns call for "scraps to equal 1 yard" etc. An easy way to figure out how much you need is to count the number of squares, rectangles, etc of each size you need and cut that many from your scraps. You don't have to add up yardage that way. I have one scrap pattern that I do regularly. I don't remember how many yards of scraps it calls for but I know that I need 88 five inch squares and 176 four inch squares. I know I need a scrap big enough to cut 1 five inch square and a scrap big enough to cut 2 four inch squares.