Look at the per unit price!
When we shop, we always look at the per unit price. Not all stores list it, but when they do it is in smaller print on the shelf price tag. Depending on the item it will be $/100ml, $/g, etc. These prices not only help you make informed decisions comparing generic vs branded items, but I’ve seen the larger packaging of the same item be more expensive, even though you assume it should be the same price or less! Sometimes there isn’t a benefit to buying the larger package. Buying based on the per unit price helps to avoid over buying, over spending and wasting!