I agree..... it's really hard to determine the exact amount of fabric to use. On the OBW that I made I just bought 6 times the repeat. My repeat was 24", I think. And my hexis were about 6" across. With 1/4" off each edge, it does add up. Here is a picture of my quilt. I added a wide border to make it big enough for my full size bed. But if your repeat is a good size, I would think that getting 12 times the repeat would be enough. And just a suggestion for those of you that haven't purchased fabric yet, I really think that a lot of variation in color makes the best OBWs. My fabric's pattern was too much of the same color.... I won't make that mistake again. I'll buy the ugliest print I can find with lots of color.

OOps. That's a picture of my OBW before I stitched down the applique and quilted it. But, you get the idea, right? The skinny border outside the pink border is the original fabric. You can tell, it's too much of the same colors.