Remember that when u add a piece of fabric, you have to count two 1/4 inch measures, to account for the quarter inch from both pieces that are taken up in your 1/4 inch seam.
Then u can add the amount u want the block to be, (i.e.1/2 of the total enlargement if u are using a block with two parallel sides. If u add 1 1/2 inch to two sides of a block, the measurement of that block will be 2 inches wider. (The 1/2 inch is used to make the seam--it makes the original block 1/4 inch smaller because u used it in a seam, and 1/4 of the added piece is also used in the seam.) Hope this helps.