Actually, from what I understand (still noobish here), there is also die swell to account for. Normal filaments (ABS/PLA) exhibit a tendancy called die swell. They are under pressure behind the die and when extruded that pressure is released and the material expands slightly. I have noticed that the amount of swell is affected by backpressure on the head (thin layers typically at the beginning of the print) as well as moisture content of the filament. I noticed that I got thicker walls before I started locking up my filament in buckets with descant.

I don't think anyone will be able to tell you the thickness. There are simply too many parameters that affect it. Idler tension, moisture content, filament material, extrusion temperature, moisture content, layer height, etc.

Quote Originally Posted by soofle616 View Post
I suspect that there is a mathematical relationship between speed/feed/line width but I don't know that anyone has ever actually figured out what that relationship is.
Not sure, but I think Simplify3D has figured it out. In the extruder tab on in the FFF settings panel, there is a seting for line width. The auto setting seems to change based on layer height and speed. I don't know if temperature affets it. In my normal FFF settings for ABS, the auto setting most often reads 0.42 for a 0.35 nozzle. That meas its accounting for a 0.07mm swell. Somehow. I don't know what all goes into the calculation but clearly the folks over at S3D got something figured out.