Square in a square math
 

This is embarrassing, but I need help. I have a stack of six inch square string blocks that I want to add triangles to and make square in a square blocks. How do I figure out what size squares to cut for my half square triangles? Thanks!

Go to quiltville.com. There is a nice chart for Putting it on Point. I would use the corner triangle measurements for your square in a square.

You add 7/8 to the size block for triangles. So, if the block is six inches, 6 7/8 and then cut down the middle on the tip to tip. But you could just lay the corner piece of fabric onto the string block at the point to where the regular seam allowance is past the half way mark by a quarter inch and measure it to be sure. Some people just go ahead and add a full inch, cut the triangle, sew from tip to top, press and trim it back to square it up to size. The last way I know is to lay a matching square on top of the finished one that has a line drawn line down the center bias (tip to tip). You then sew a quarter inch line of either side of the drawn line and then cut on the line. It will then be two squares. It will have the string piece on one side and the solid fabric on the other.

Thanks y'all. Knew I'd find the help I need here!

It depends if you want the triangle ends to meet in the middle of the block or not. I glue my triangles on first before sewing because I usually get a few wonky.