I am slowly making some progress on Serendipity. I think my original estimate of 480 blocks was high. I will need 100 12 inch blocks. Each 12 inch block is made of 4 six inch blocks so that is 400 blocks. That will make the top 120" X 120". I am not sure that will even fit on my quilting machine. It is supposed to take a 10 foot top but not sure how well it will work. I may have to stick with 9 blocks by 10 blocks.