Curtains Analysis..should have listened to my math teacher!

So here I was, working in EQ with my curtains, already decided on 12" pinwheel blocks, which is a new block for me. Looked real good, size about 40" x something,  good size for (2)  4' x 5' windows side by side...leaves enough for the sunlight to still come through...

Did you know that 12" starting blocks  actually turn into 16 1/2" size pinwheels when put together? I should have realized that...since one uses 2  blocks to make a pinwheel. I really had a "duhhhh" moment!  Which is exactly why I decided to make pinwheel curtains first.  Imagine if I had already cut 40 12" blocks for a quilt.  I might not have enough companion fabric to finish it.  At least this way I am okay.

I'm sure there is an easy formula/go-by for figuring this out..just will have to research it. 

I am using the sew-around-the-edges method of making HSTs. Have made 1 so far to test the waters..

Now I'll start on the assembly line method to finish the others.

The good news to all this is that I will need less pinwheels. Instead of the 18 blocks, I am figuring on 15, possibly even only 12 needed.  Maybe I won't have to cut any more!