That's not as much of a problem as it may seem - we are looking to get the cost per bar, so we need to know the cost per batch, so we need to know:
1 - cost of ingredient per unit
2 - number of units of ingredient used per batch
3 - 1 multiplied by 2 for all ingredients
4 - all of the 3's added together
5 - bars per batch
6 - 4 divided by 5
6 being the final cost per bar.
Whatever unit is must be consistent but only per ingredient. We might measure Olive oil in Oz but EO in bottles - we might use 50 oz of olive oil and 5 bottles of EO per batch. When working it out, we can stick to these two units for these two ingredients with no issues at all. There is no need to convert all units to one unit at all:
Batch cost = (cost of olive oil per oz * 50) + (cost of eo per bottle * 5)
We need to convert units only when we measure an ingredient in to a batch in a different unit than how we buy it - I buy my olive oil in litres and use grams of it in my batches. Therefore I need to work out item 1 in my list above as the cost of olive oil per gram as I put grams in to a batch.
When people are selling, they should also work in the cost for labour, which is another unit as well!
As long as we accurately record the cost per unit and units per batch, regardless of these units actually are, we will get to the costs.
