Can you spot the cheapest supermarket prices?

You’re in the supermarket fizzy drinks aisle, looking for the cheapest Diet Coke. 

Sounds simple, right? But a single can is one price. A multipack another. Further down the shelf, you spot three differently sized bottles with more prices to consider. And that’s before loyalty discounts or multibuy offers. 

If you're confused, you're not the only one. Our latest investigation has found that 72% of people couldn’t spot the cheapest fizzy drinks in a range of real-life examples from supermarkets* – while the video above shows how confused people were when faced with the challenge of finding the best-value option when we took the quiz on the road.

This is troubling during a cost of living crisis – particularly given that our research shows you could pay up to 346% more by going for different sizes of exactly the same product.

How supermarkets are letting shoppers down

With the current cost of living crisis, clear pricing for food and drink is more important than ever; yet we’ve discovered supermarkets are letting shoppers down.

Our investigation found unit pricing – which enables you to compare value by the cost per unit (for example per 100g or 100ml) – is often unclear, inconsistent or absent.

Supermarket shelves are often full of different-sized versions of the same groceries. The common belief that bigger generally means better value is often true – but that’s not always the case. This is where unit pricing is a shopper’s saviour. If you know the price per 100g or 100ml, you can see which is the cheapest straight away.

Can you spot the cheapest fizzy drinks?

Take the quiz below to see if you could pick out the best value deal and avoid the most expensive option.

The huge savings you could miss

We compared the average prices of 10 types of popular groceries for three months (1 March to 31 May) in the UK’s four biggest supermarkets (Asda, Morrisons, Sainsbury's and Tesco). We then worked out the price per 100g or 100ml to check how much more you could be paying for different sizes. The results were stark. 

The price of Coca-Cola per 100ml varied between 11p and 50p at Tesco. That’s 346% more for a shopper who buys four 250ml glass bottles compared to one who picks a 1.5-litre bottle instead. 

For Walkers Ready Salted Crisps the price per 100g varied from 57p to £1.89 at Asda. So, 231% more for a shopper buying a 45g packet than one buying a 175g sharing bag.

And it’s not just the big brands. For own-label semi-skimmed milk, the price per 100ml varied between 6p and 13p at Morrisons – that’s 133% for a shopper choosing a 500ml bottle than one picking a 2.27-litre one. 

Of course, not everyone can use bigger sizes because of the storage needed and the risk of waste. But the right information is essential for making budgeting decisions.

• ​​​​Find out more: which is the cheapest supermarket? 

Unit pricing is confusing, inconsistent or missing

Supermarkets are legally required to provide unit pricing on most items under the Price Marking Order 2004. But even when supermarkets stick to the rules there are still gaps that create confusion for shoppers.

We trawled nine major supermarket stores (Aldi, Asda, Iceland, Lidl, M&S, Morrisons, Sainsbury's, Tesco and Waitrose) to see how unit pricing is working in practice – and found a multitude of issues. 

The gallery below shows some of the worst examples we came across in stores.

Different units were used for the same types of items – for example, some tomatoes were priced per kilogram while others were priced per tomato. 

There was also confusing terminology; such as for peppers in Lidl, which were priced both per ‘piece’ and ‘each’. At M&S, ‘each’ was used to mean both a pack of four pears and also per pear, depending where on the shelf you looked. 

We couldn’t find unit pricing on any special discounts for loyalty scheme members, or on yellow sticker items reaching the end of their shelf life. The information was also missing on many promotional displays – such as a big stand of Cadbury’s sharing bags in a Morrisons store. 

Then there was unit pricing that was hard to read, as with the faded label on bananas in the Waitrose store we visited. Or where it was obscured completely, such as on tomatoes in Morrisons (another label had slipped over it), and on confectionary in Iceland where it was covered by a promotional banner. 

There were numerous examples of unit pricing missing entirely – including on a pack of tomatoes in Tesco, Penguin bars in Waitrose, some soft fruit in Morrisons and on vine tomatoes in M&S.

Why multibuys are so confusing

There are also big differences in how supermarkets present and use unit pricing online, particularly for promotions. 

We looked at nine major supermarket websites (Aldi, Amazon Fresh, Asda, Iceland, Morrisons, Ocado, Sainsbury’s, Tesco and Waitrose) and found they all displayed unit pricing for standard priced items and for discounted items. But we couldn’t find unit pricing for multibuys at any of the supermarkets (though not all stores sell them). 

Tesco was an exception because so many of its discounts are now offered through Clubcard Prices, and it doesn’t display unit pricing on these. That means most discounts in Tesco, both online and in-store, don’t have unit pricing,  which could make it hard to compare prices at the store. 

• Find out more: loyalty cards compared 

What the supermarkets say

We put our findings to the supermarkets, and two replied.

A Waitrose spokesperson said: 'We regularly review all our products to ensure our unit pricing is clear and consistent so that customers can compare prices and save money. Our Partners are always on hand to assist customers with any pricing queries.'  

A Lidl spokesperson said: 'We always endeavour to ensure that pricing information is as clear as possible for our customers so that they can make informed purchasing decisions.'

Which? calls to improve pricing

Which? has campaigned on the issue of unclear pricing before, culminating in a super-complaint to the Competition and Markets Authority in 2015. 

That led to a series of recommendations to improve unit pricing in supermarkets – but the legislation itself wasn’t changed and our latest research shows there’s still a lot more to be done.

Which? believes clear unit pricing is key to helping shoppers through the current cost of living crisis and is calling on supermarkets to urgently do more by making unit pricing more prominent, legible and consistent – as well as by displaying it on their promotional offers. 

• Find out more: free advice to help with the cost of living 

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*In June 2022, we carried out a nationally representative survey of 2,000 UK adults.