You measure the circumference of your quilt, so the total of all four sides, ie a 60x80" quilt would be 280". Divide this by the width of your fabric, I use 42" as an average, this gives you number of cuts you will need to make, 280/42 = 6.66, so you need 7 cuts. Now each cut is 2.5" so multiply the number of cuts by the width, 7 x 2.5 = 17.5" or 1/2 Yd. I'd get a little more just to be safe, I've been known to make incorrect or not straight cuts. I've explained in full rather than just give you the numbers so you will know how to do it next time. I hope that helps.