That is a very complete (and complex) spreadsheet, aiming to suggest the proper choice of weights.
If the goal is just to determine the required lift of your BCD, you do not need to know how much lead you will need, as the BCD should only compensate for buoyancy VARIATIONS...
Such variation has substantially just two origins:
1) the weight of gas in your cylinder(s), which is known with great precision (it is roughly 1.2 kg/liter after expansion)
2) the loss of buoyancy of your diving suit, which is roughly your weight divided by 100 and multiplied for the thickness in mm (for a 50m maximum depth).
After computing your buoyancy variation, just add 3 to 5 kg for safety, and that is the required lift of your BCD.
