What I have gathered from Bonnie Hunter's website is that a brick is a rectangle which is the equivalent of 2 squares of the width sewn together. In case that is clear as mud, let me give you an example: a brick with a width of 2" would have a length of 3.5"; 2 2" squares sewn together would be 3.5 inches -- 2 + 2 = 4 - .5 (seam) == 3.5. A brick with 3.5" width would need to be 6.5" long, etc. Only my understanding --- I could be way off in left field!!