What units should the quantities be in my Bill of Materials (BOM)?

The units in your BOM quantities should be how much component is used in ONE unit of the finished good (that the sale order is recorded against). The units must be consistent across the whole BOM structure.

For example, if you have a drink that uses 20g of lemon concentrate, and you sell each one separately, the BOM quantity of the lemon concentrate should be 20. The units must be consistently in grams.

However, if you sell these in cartons of 5, and the sale is recorded against the carton, you could create a separate SKU, with another BOM line item, for the carton and the drink with a BOM quantity of 5. So then the system will calculate a sale of the carton as effectively 5 * 20 = 100g of lemon concentrate in a carton.

Or else, if you never sell the drinks individually and you plan for only the carton, and the sale is recorded against the carton then you could set up the BOM item directly between the carton and the lemon concentrate with a quantity of 100g.