Convert both package quantities to the same unit, then divide each delivered total by that quantity. For example, compare price per kilogram with price per kilogram, not one item's price per 100 grams against another's price per pound.
Check whether the packages really contain equivalent products, strengths, or usable amounts. Shipping and fees can erase a bulk discount. A larger pack may waste money if it expires or goes unused. Use a unit converter when labels differ and keep the calculation visible.
The lowest unit price is a useful signal, not an automatic buying decision.
Akousa