Here's a guide/tutorial/paper on my sizing workflow for Daz3D,

http://www.renderosity.com/mod/freestuff/?item_id=75531

English Bob has an excellent little tutorial on the various sizes in different programs,

http://www.morphography.uk.vu/tutorials.html

I don't bother with the math, I just use a 'dummy' as a size reference when building stuff in Blender so that it looks right and properly proportioned in Daz3D or Poser.  What kind of stuff are you making?  I've gotten pretty good in Blender and want to make some items for  'Podaz' (Poser and Daz3D), then move into a line of ornate gowns for the ladies.  Along the way I'm making a comprehensive guide.  I'm much further along with the Poser guide.