You know, I find myself a bit puzzled now. The standard conversion I have learned is that going from DME to LME you need 1.25 as much. When going from LME to DME, you need 0.8 times as much (which is 1/1.25).
However, in "How to Brew", it mentions that DME has about 40 points per pound, whereas LME generally has 36 points/pound. And as an example, the book states that 5 lbs of DME and 5.5 lbs of LME will both achieve the same OG.
So maybe Revvy deserves some love here?
Has anyone actually measured typical extracts for their actual gravity properties? I would guess there is some variability. Palmer's book also states that DME typically runs 1.40 to 1.43 per pound in a gallon of solution, suggesting that perhaps 41.5 points is the correct mid-range, whereas LME runs 1.34 to 1.38 (consistent with the 36 points for LME bogey).
At any rate, like many others have suggested, the actual OG generally has to be equal to what you put in divided by the volume of solution. Unless your extract was bad or diluted somehow, your OG should be in the range of 1.56 (using 36 points for the LME in 5 gallons total wort and 7.5 lbs of LME), or 1.051 if you finish with 5.5 gallons into your fermentor, which is a common volume for brewing 5 gallon batches.
I am also guessing there are steeped grains providing some fermentables in this recipe as 7 lbs of DME in 5 gallons only gets the OG to 1.058.
When you transfer the wort to the fermentor, it's a good idea to pour the wort back-and forth between the fermentor and the boiling pot, or shake it if in a carboy. This will help homogenous the solution as well provide some oxygen for the yeast. It should also provide and almost foolproof way of reading your OG correctly.
