blocks very seldom (finish) as a 1/2"....the 1/2" is the seam allowance before being joined with other blocks/sewn into the quilt...we would need to know the block to figure out the math for it- but (basically) to enlarge (or decrease) the size of a block you first subtract the seam allowance amount- then increase or decrease as needed- then add the seam allowance back in---an example...if you wanted to double the size of a block with pieces that are 2 1/2" to start- you would subtract the seam allowance (now 2") double it---to 4" then add the seam allowance back on- so cut 4 1/2".