You'll need to know the overall size of your quilt and then decide how big you are going to cut your initial squares. I usually cut my squares 6 1/2" for a D9P which means that I will be able to get six squares for every 6 1/2" strip of fabric I cut. One strip of each colour chosen would yield 54 squares which would make 6 nine patches. These nine patches would originally be 18 1/2" before cutting and after cutting would be about 17" resulting in a row of 102" long. You'd need five completed strips for a top of 85" X 102" approximately. Going back to my original math means that I will need to cut five 6 1/2" strips of every colour which is 33". Of course I'd buy one yard to allow for cutting errors. Nine yards will make your top. I hope this helps.