Field note 06 / 24·4 min
Find value beyond the big pack
Price per kilo, litre, or use can cut through a crowded shelf.
Put prices on the same basis
Divide the price by the quantity to find a unit price. Compare the same units: a price per 100 grams needs converting before you compare it with a price per kilogram. The larger pack or brighter sale label does not automatically offer the lower unit price.
Count what you will actually use
A lower unit price helps only if the product meets your needs. Check quality, concentration, storage, expiry, and waste. A detergent with a different concentration may need a comparison per recommended wash; a food you throw away has a higher cost per useful portion.
Include delivery charges or extra travel required to obtain a deal. Avoid increasing the purchase simply to reach a discount threshold unless the additional items are useful. This is a comparison method, not a reason to always buy the cheapest item: dietary needs, accessibility, reliability, and your available cash still matter.
Two packs, one fair comparison
A 750 g pack costs 3.60, or 4.80 per kg. A 1 kg pack costs 5.00. The smaller pack has the lower unit price. If half the smaller pack would go unused, its lower shelf comparison would still not guarantee better value for you.
Illustrative numbers, in consistent units.One thing to try
Compare two products you already buy. Write both prices per kilogram, litre, item, or useful use.
A 500 g pack costs 2.40; a 1 kg pack costs 5.20. Which has the lower price per kg?
Source notes
These references support the general principles. Product terms and legal protections vary by country.
- Unit prices for groceriesAustralian Competition and Consumer Commission · Checked 2026-11-03
For general education. Examples do not include every fee, tax, personal circumstance or local rule, and are not individual advice.