http://www.sunshinequilts.com/borderfit.pdf

*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
Example:
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.
Example:
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