Compare the same quantity
A pack price supports fair comparison only when you know how much product it contains. A 500 g packet costing three euros equals six euros per kilogram. A 750 g packet at four euros equals around 5.33 euros per kilogram. The second has a higher total price but a lower price per kilogram. These are different questions: what you pay now and what a comparable quantity costs.
Calculate with the unit visible
To obtain price per kilogram, divide price by weight in kilograms. For a 250 g pack, use 0.25 kg. Two euros divided by 0.25 gives eight euros per kilogram. For liquids, compare per litre when meaningful and when products are comparable. Do not mix millilitres and litres without conversion. Writing the unit beside each number reduces mistakes a mental calculation can hide.
When comparing by use makes more sense
Some products are presented as items or doses and need another check. Ten pieces for five euros equals fifty cents per piece, but does not resolve differences in size, quality or purpose. If a manufacturer specifies a dose, check what it represents before comparison. The aim is a common measure describing actual use. A smaller number on a label may simply refer to a smaller quantity.
The larger pack does not always meet the need
A cheaper price per kilogram may be impractical if you cannot use the contents. Consider space, frequency of use and existing supplies. Unit prices organise information but do not decide for you. For food, read storage requirements and relevant dates. When comparing different products, include important characteristics without pretending division removes every difference between them.
An exercise for your next comparison
Choose two sizes of the same product and note price, quantity and reference unit. Calculate and check whether your result matches the shelf label where one exists. If it differs, first review conversion and which product the label refers to. Preserve the reasoning rather than memorising prices, which change. The useful habit is explaining the comparison and recognising when information is missing for a sound conclusion.
