OK kids. 5th grade fractions to percentage. Divide what you want by what you have--so if you have an eight inch square that you want to change to a ten inch, you divide 10 by 8 and get 1.25. Move the decimal over and enlarge by 125%. If the pattern came with a seam allowance THIS WILL MESS IT UP. Cut out the new pattern(lose the old seam allowance), trace it on graph paper and draw a new seam allowance. Yes you will have to use a tape measure on the curves. I think patterns don't come with fabric quantities because if you modify them at all, the quantity will change. I just make a generous guess and add to my stash a lot.