Does this sound familiar?
Well, it’s been a long time since I’ve had to do any geometry theorems. A really long time. So I really had to dig deep to figure out how to find the finished size of the Rubble Pillow from any starting size of square. *Check out the directions under “Classes and Workshops” tab.
My recollection was very vague (my last geometry class was in 1976!). So I sought out the expertise of my favorite retired Seattle Pacific University mathematics professor, Janet Buck. We sat in the balcony of the church one Sunday morning and she verified my logic and told me I was, indeed, doing it right. So here it is.
Both of the measurements for “a” and “b” are going to be ½ of the measurement of the starting side less the ½” used in your seam allowance. We are using a square, so “a” and “b” are the same measurement. So, take ½ of the side measurement, subtract ½” seam allowance and square it (times it by itself). Then, double that number and find the square root of that. Your phone will have a calculator that will do these calculations! This will be your finished pillow size!
For example: starting square is 20” on each side
2(9.5 x 9.5)=180.5
Your finished Rubble Pillow will be a little less than 13 ½”.
Go math nerds!