Finding the repeat is quite simple. Look along the selvage edge to see an easily identifiable section of the print. then look down the length of the fabric until you see that same section - that's your repeat length. If you're making hexagons - you need 6 repeats or if octagons - then you need 8 repeats. I always buy more so have enough for whole border sections. I don't usually know when I buy the fabric if I'll use the original fabric for the border, but I buy it then, to make sure I have it if I need it. Also buying a hinged mirror (mine is made by Collins), is very helpful to decide if a fabric you're considering would be a good choice or not, to make kaleidoscopes. If ordering online and they don't tell you the repeat length, send an e mail to ask, or include that you need 6 repeats or whatever , when you place the order. I've done that and they sent me an email back that there wasn't enough to send me 6 repeats. In one of the books for OBW, they mention to not use a fabric that has more than 6 colors, because they don't work well. Wrong, I used a fabric that had more than 14 colors and it's wonderful. The print is the main thing to look for and preferably make sure the background is not a solid color, or if it is, there shouldn't be very much in comparison with the printed area. The background should have swirls of color or the fabric shouldn't have a background, in other words it should be all print. None of the fabric stores I shop in, complain when you ask to unroll a bolt to see the repeat length. If they did, I wouldn't go there again.