Welcome to the Quilting Board!
*shudddder* mmmmaaaathhhhh I'll just send mine to you Sassy LOL
So far all I have done is made continuous bias binding for my borders. Here's the formula for figuring it out (it's easy math).
To calculate how much binding a square of fabric will produce:
length = area of square divided by width of binding strip
For a 20" square, area = 20" x 20" = 400" square inches
binding strip width = 2"
400" square inches area divided by 2" width = 200" binding
To estimate how large the square must be to produce the binding length you need:
1.Multiply the length of the strip needed by its width to find its area.
2.Determine the square root of the area to estimate the square size needed.
Strip needed is 2" wide by 250" long
2" x 250" = 500" square area
square root of 500 = 22.36
Round up and cut a 23" fabric square