I know I am a little, well a whole lot, late with this response but I found this on a blog, not sure if it is what you were looking for.
Fitting patterns to the stock you have.
Instead of resorting to trial and error, use simple math to increase or reduce the size of a pattern to fit your stock. Divide the size of the stock by the size of the pattern and multiply by 100. If your stock is 15" and your pattern is 18", this will equal 83%. Simply photocopy the pattern at 83% to produce a pattern that will fit your 15" stock. If your stock is 18" and your pattern is 15", you?ll want to photocopy the pattern at 120%.
By Loren Solbreken, scrollsawer.com forum