Now that you have reached this page, you have probably found what you are looking for: an easy way to calculate fret spacing. That is wonderful, I hope you find this page very useful. I, however, would much rather have you looking at my new development. Please visit FretFind 2D.
This page should allow a person to quickly and accurately calculate the information needed to design the fretboard of a stringed instrument. Remember to use like units for all the measurements!