Mitered Borders -- Magic Formula?
I want to sew several narrow borders together to create one wide border and then miter my corners. This is going to be scrappy. I'm trying to figure out if I have enough of each color family of fabrics. Is there a magic formula to know how much extra fabric you will need to miter the corners. In my head, I keep thinking I will need the width of the overall border on each end in order to miter. I can't find any confirmation of this out in cyber space and I have no idea why I'm thinking it.
So math folks, what do I need?