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.