Hi..

I just posted elsewhere (it's about a type of purer, better tasting stevia), and it seems related and/or useful

http://forum.lowcarber.org/showthread.php?t=226564

There are 2 different conversion listings (this will make more sense after reading that post)
The bottom of this page:
http://www.nunaturals.com/products/sooolite.html
And here:
http://www.sooolite.com/pdf/sugar-equivalent-table.pdf

To convert splenda to stevia, I usually convert splenda back to sugar, then sugar to stevia.