Terrific free online calculator
 

If you know one component of a square in a square block and need the size of another component, this is terrific http://www.quiltersparadiseesc.com/C...Calculator.php

Wow, that is a great calculator. I was going to make Sq in a Sq blocks and didn't know what size triangles to add to my 6" blocks. So easy and helpful. Thanks for posting the link!

I'll have to bookmark that one. Looks like a handy calculator to use! Thanks for sharing.

Wow! Thank you this will be very useful and so very quick! I am going to give it a try!

Watching a video from Teresa Down Under, she cut a square the same size as the original center, placed it on top the original center, and sewed around all four sides, with right sides together. Then marks an 'X' across the top wrong side and carefully cuts through the top layer to make her square in a square.... it works after a fashion. On half square triangles, I figure the size I want and add the seam allowance. That is an Eleanor Burns suggestion in making them from selvage to selvage ruler marked HST Bloc Loc makes a template to square it up in standard pattern size that works for me.