How to use the unit price on a supermarket shelf label to spot the better buy
The small print under the big price tells you what you are really paying per kilo, litre or item. Here is how it works and the traps to watch for.
The biggest number on a shelf label is the price of the pack in front of you. The more useful number is often the small one underneath it. That is the unit price, and it is the quickest way to tell whether the big bottle, the multipack or the "special offer" is actually the cheaper way to buy.
What the law says
Shops in the UK have to follow the Price Marking Order 2004. It requires them to show the selling price of the goods they sell, and for most food and household goods sold by weight, volume or length, to show a unit price as well. That is the price per kilogram, per litre or per metre, and for some smaller items it may be shown per 100 grams or per 100 millilitres.
The point of the rule is to let you compare products of different sizes on equal terms. Some smaller shops are exempt from showing unit prices for many products, so you will see them most consistently in larger supermarkets.
A quick example. Say a 500g bag of pasta costs 90p and a 1kg bag of the same pasta costs £1.50. The labels should show:
- 500g bag: £1.80 per kg
- 1kg bag: £1.50 per kg
The bigger bag is cheaper per kilo, so if you will use it before it goes off, it is the better buy. The unit price saves you doing the sum in your head.
Where it gets tricky
The idea is simple, but a few things can make comparisons harder than they should be.
Different units on neighbouring labels. One product may be priced per 100g and the one next to it per kg. Check you are comparing like with like before you decide.
Items priced "each". Some goods, such as toilet rolls, dishwasher tablets or eggs, are often unit priced per item or per sheet. A pack of nine "long-lasting" rolls is not easy to compare with a pack of twelve standard ones unless you look at the price per sheet, where it is shown.
Offer prices. When a product is on promotion, check that the unit price on the label reflects the offer price. If it does not, you can work it out yourself or ask a member of staff.
Loyalty prices. Many supermarkets now show two prices: one for everyone and a lower one for members of their loyalty scheme. Look at which price the unit price refers to.
Bigger is not always cheaper. Multipacks and family sizes are often the cheapest per unit, but not always. Smaller packs on promotion sometimes beat them, which is exactly why reading the unit price is better than assuming.
Getting into the habit. You do not need to check every item. The categories where unit prices make the most difference tend to be the ones with lots of pack sizes: cereals, rice and pasta, tea and coffee, cleaning products, nappies, pet food and toiletries.
Online, most supermarket websites show the unit price beside each product, and you can often sort search results by price per unit rather than by pack price. It is one of the quickest ways to cut the cost of a weekly shop without changing what goes in the basket.
A word on waste. The cheapest price per kilo only saves money if the food gets eaten. A large bag of salad that ends up in the bin costs more than the small one you finished. For fresh food, buy the size you will realistically use, and save the bulk buying for things that keep.
