I love math, but when quilting is involved - I want to get at it quickly. EQ7 is my friend. I bring up the block design and build my quilt on the computer. If I want it bigger, I change the block size and wala. If I want it smaller - same.
I add borders - subtract borders and change sizes in a flash. Then I go in and put a color where I plan for each fabric. They become color 1, 2 etc. Then I click on print yardage requirements and it gives me a picture of the quilt, a list of fabrics and how many pieces of each one I need along with total yardage of each. I have no affiliation with EQ but have used their program for many years. The updates are just like housing and food as far as my budget is concerned. Check out their website. I also have a youtube on the slip and slide method for backs that will help in saving fabrics as well as making it easier for your longarmer to keep that back flat during quilting.
https://www.youtube.com/watch?v=fsAyGYSXY78 I am no longer affiliated with Quilt Supplies for U but if you want the excel spread sheet for calculating backs for the slip and slide technique email me and I'll be happy to send it to you. John Flynn is the person who came up with the formula, I just put it into a spread sheet because I'm lazy about doing it over and over.
Happy stitching.