Help Adding Grains - Potential SG

I'm trying to create grain entries for Briess Pilsen DME and Muntons Extra Light DME. I have to admit I'm a little surprised that they are not included by default.

If I look at the PDF specs for Briess Pilsen, it gives these details:
Fermentability: 75%
Desired OG: 1.040 = .89lbs/gal - 2.5 for color
Desired OG: 1.050 = 1.11lbs/gal - 3.0 for color

so, when I try to add this to beersmith, I understand what to put in for color. But if I use 75% for the fermentability, beersmith calculates 1.034 for a potential SG. Using the specs above, I would expect it to calculate 1.045. I don't get it - what am I missing? I want to add these correctly.

Thanks,

Jason

What you are missing is that there isn't a place for fermentability for anything.
Yield is not fermentability.

I wish there was a spot for fermentability but there's not.

Fermentability is the ability of the yeast to attenuate the sugars into alcohol.  75% is typically the best you can do, such as OG=1.040  ==> FG 1.010.  That is 75%. 

The calculation to get Potential or [Point per Pound Gallon (PPG)] is  [ (1.040 - 1)Pts  / 0.89lb ]  +  1  =  1.045
using the other example  [ (1.050 - 1) / 1.11 ]  + 1  =  1.045

The same 

Happy Brewing, David

"Fermentability is the ability of the yeast to attenuate the sugars into alcohol."

Yeast attenuation is not the same as fermentability. Fermentability is the ability of sugar to be fermented.
When you mash you create fermentable and unfermentable sugars. Also your ingredients provide sugars that are more and less fermentable. Adding something like maltodextrine provides sugar that is 100% unfermentable to the wort. Cane sugar is 100% fermentable to the wort.
Briess has figured out the fermentability of the worts they sell as extract and list them. It sounds like the OP is confusing this with yield.

Personally I have my doubts about yeast attenuation being the driving force behind final gravity.
I've read of people doing tests with cider and one of the yeast was WL002 with an attenuation of 63-70%, FG was 0.998. Even if it was WL007 it shouldn't have gone that dry if attenuation was the driving force.
It would be nice for us cider makers if getting a 1.012 finish was as easy as yeast selection but it doesn't seem to be happening.

Try a test. Your 75% attenuating yeast against nothing but cane sugar, water, nutrient and energizer. Or try it against wine grape juice. I bet it goes dry.

Point made and taken, though I would have expected a high percentage of fermentable sugars in DME.
The potential calculations are correct 
I have made wine and gotten SG reads less than 1, but there is also the alcohol density to consider

If I remember correctly I think Briess says 78%, 80%, 85% between Dark, Amber and Light.

When I was extract a long time ago I always had very good results using a list from Papazian's "Companion" and ignoring attenuation. Back in those days it was well known what extracts were more and less fermentable even if the percentages weren't published. Being from those days and the success I had predicting with a list, pencil and paper I am amazed BeerSmith ignores fermentability and only uses attenuation. Just because there's not a formula there seemed to be an accurate list almost 20 years ago.
The lack of a fermentability entry really screws with me making sweet stouts trying to predict final gravity without going back to "The Homebrewer's Companion" and paper.

Personally, I use just the generic DME/LME values.  After all, extract is basically the same from everyone.  I think that the minor differences between them will be subtle and only make a couple points difference.