Keep in mind that once you stuff your biscuits they will be much smaller so you'll need more biscuits to cover the area that you need. A friend of mine made a quilt and didn't take this into consideration. She calculated the overall size of the quilt based on the size of her squares. Her twin size quilt turned into a lap quilt if even that once she stuffed her biscuits. You might want to make a sample with say four biscuits by four biscuits and measure the size before and after to give you an idea of how many squares you will need to get the size you want. Once you have that it is easy to calculate the amount of fabric.