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ELI5 Yahaaa

The number under the price

Which Packet Is Actually Cheaper?

Comparing packets means dividing until both are the price of the same amount.

Small packet £1.80 for 300 gLarge packet £4.20 for 750 g
Neither price tells you which is cheaper until you divide.

  1. Step 1 of 5

    Two prices for two sizes compare nothing.

    Cheaper packet Costs less to buyCheaper food Costs less per gram

    A bigger number can be better value and a smaller number can be worse. The prices are answering different questions.

  2. Step 2 of 5

    Dividing makes them the same question.

    1 £1.80 ÷ 300 g2 0.6p per gram3 £4.20 ÷ 750 g →0.56p per gram

    Cost divided by amount gives the price of one gram, one litre, one sheet. Now both packets are described in the same words.

  3. Step 3 of 5

    The bigger packet usually wins, but not always.

    Small packet0.60p per gramLarge packet0.56p per gramSmall, on offer0.47p per gram

    Packaging and handling cost roughly the same whatever the size, so they are spread thinner in a big packet — until an offer flips it.

  4. Step 4 of 5

    Value is not the same as saving money.

    Used entirely The unit price was realHalf thrown away The unit price doubled

    Better value per gram is only cheaper if you use it all. Half a wasted large packet is the most expensive option on the shelf.

  5. Step 5 of 5

    Which is why shelf labels carry it.

    The shelf label The small print is thehonest number

    Shops are required to print the unit price precisely because two prices for two sizes are so easy to compare wrongly.

    Watch for units changing between labels — per 100 g next to per kilogram is a comparison waiting to go wrong.

The short version

Unit price divides cost by amount so different sizes can be compared, but it only tells the truth if you use it all.

Try it yourself

Take two sizes of the same cereal and check whether the bigger box really is better per 100 g.

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