Square in a Square calculator

I recently stumbled across a simple calculator for square in a square blocks on the internet.  Don't get me wrong -- I love math!  But rather than go back and figure this out again, or find something in my files, I hit the internet.  

Quilter's Paradise has developed a simple square in a square calculator.  You either enter the inside square or the outside square and their formula calculates everything for you! To get there, click on this link:

Square in a Square calculator from Quilters Paradise.  

I was trying to figure out the pieces for a 6" inner square and 12" second outer square.  Here's what the calculator gave me:

The first result is for the 6" inner square:

The second is for the 12" outer square:

Now, I can confidently make the blocks I need for an interesting quilt that starts with a double square in a square block.

I hope you can use this calculator too!