Guide · Shop smarter
How to compare grocery prices fairly using unit price
The biggest pack is not always the cheapest per gram, and the "sale" pack is not always a sale. Comparing by unit price is the quickest way to know what you really pay.
The basic idea
Unit price is the price divided by the quantity. A 500 g pack at 2.50 costs 0.50 per 100 g. A 750 g pack at 3.30 costs 0.44 per 100 g, so it is cheaper per gram even though it costs more in total.
Step by step
- Pick one common unit: per 100 g, per kg, per litre or per 100 ml.
- Convert each pack to that unit. Keep grams with grams and millilitres with millilitres.
- Divide the price by the amount, then multiply to reach your common unit.
- Compare the final numbers. The lower number is the better price per unit.
Things that can mislead you
- Shrinking packs: the same price with less inside is a hidden price rise. Check the weight each time.
- Multi-buy offers: "3 for 2" only helps if you will use all of it before it spoils.
- Loose versus packaged: loose produce is often priced per kilo, packaged per pack. Convert both.
- Shelf labels: many shops print a unit price on the tag, but different items may use different units, so check.
When the cheaper unit price is not the better buy
Bulk only saves money if you use it. Fresh food that goes off, or a product you do not like, costs more than a smaller pack you finish. Storage space and your budget this week count too.
Use a calculator
The Daymark grocery comparison calculator does the conversion for you across several products, so you can compare at the shelf or while planning a shop. It runs in your browser.