Book excerpt: In the Quilty Math Workbook, I'll walk you through calculating exactly how much fabric you need for your next quilt. I've got all the formulas figured out. You just need to fill in the blanks with the specifics of your quilt and punch those numbers into the calculator. The Quilty Math Workbook can be used to design your own geometric quilt or calculate exactly how much fabric you need for an existing quilt pattern.