The general back of the napkin formula is:
Delta_pH = mEq's/(BC x Kg)
Where:
BC = buffering capacity, in units of mEq/Kg_pH
Kg = Kilograms of grist being mashed
Delta_pH = pH_Initial - pH_Target
mEq's = the number of milliequivalents of acid or base required to move the pH to the target.
Some...