I have had the same problem. Didn't realize it until I had sewn many blocks and in squaring them up, they weren't the right size, were too small. I was using a new sewing machine with a 1/4" foot with flange. I stupidly assumed that it would be the proper 1/4", not so! I used the method mentioned my someone else here, with the index card, and then I took it a step further and moved the needle one thread more to the left for the SCANT 1/4" which makes up for the "turn of the cloth" taken up when the seam is pressed. You would not believe how far off I was, I had to move my needle WAY over, in fact all the way it would go! I use a Janome Horizon and now use the Accufeed foot when I piece. I was amazed how far off I was....and of course, as you probably know, even if you are off use one needle's width, it compounds according to how many seams are involved, and in the end you are missing 1/8 - 1/4" all the way around the block. Very frustrating! I thought I was crazy! Even using the SCANT 1/4" seam, I barely come out with the right size block, but it is a big improvement. Who would have imagined sewing a perfect 1/4" could be so complicated??? Once you get it though, you've got it! Best of luck to you, really play with the index card and the sewing of strips and measuring...the strips will help you determine how much you need to move the needle further to accommodate the turn of the cloth, which is also very important as it does take up space. Let us know how it goes.