My original gravity was about 1.050, after fermentation it was about 1.020? I hope this helps.
Some formulas:
Alcohol by Volume = (OG - FG)*131 = 3.93% ~ 4%
Atenuation = sugars converted/original sugars = (OG - FG)/OG in points = 30/50 = 60%. About average. Teensy bit low.
My newbie advice. (And I warn you in advance I might not know my ass from my elbow.) Is that if you want 6% beer made with 60% attenuation then you want the original gravity the *potential* for 100/60 * 6% = 10%. 10% *potential* is 10/131 = .076 so you want an O.G of 1.076. (O.G. of 1.076 with attenuation of 60% means final gravity of 1.030. og -fg * 131 = 6%)
Increase your grain bill by 76/50 or 12*76/50 = 18 lbs.
Hmmm. *That* doesn't seem right, does it.... There's probably someway to get higher attenuation than 60%. And you can probably increase your mashing efficiency.
Grain is has roughly 35-38 units of extractable sugars (lets say 37). These "units" are points per pound per gallon or in other words there is enough sugar in a pound of grain to raise 1 gallon of water 37 gravity points. Thus 12 lbs has the *potential* to extract 12*37 = 444 of these units. This is enough to raise five gallons 444/5 = 88.8 pts or an original gravity of 1.0888 but you will *not* get this. No human being ever will.
Instead you got 5 gallons and 50 points or 250 of these 444 units so your efficiency was 250/444 = 56% which isn't great but isn't terrible either. But really isn't great. Usually one shoots for 75%.
75% would give you .75*444 = 333 of these units 333 units/5 gallons = 66.6 gravity points or an OG of 1.067. 60% attenuation would mean .6*67 = 40 gravity points converted for a final gravity of 1.027 and a final ABV of 40* 131 = 5.25%
You need bigger beers and higher attenuating yeasts for higher alcohol.
But then I'm still a newbie.