The Packet Got Smaller and the Price Didn't: A 2026 Guide to Supermarket Unit-Price Trickery

Nobody sends you a letter when a cereal box drops from 500g to 450g. There is no announcement when the toilet rolls get a little narrower or the bag of pasta quietly loses 25g. The price on the shelf looks familiar, the packaging looks familiar, and yet somehow the basket costs more. That is shrinkflation, and it is not your imagination.

Here at Budgeting Is a Challenge, we are not going to pretend this is some dark supermarket conspiracy. Manufacturers and retailers have always tinkered with pack sizes, recipes and promotions. But in 2026, with household budgets still tight, it pays to notice when the packet is doing the heavy lifting. You do not need to become a full-time price detective. You just need a few habits that make the tricks harder to miss.

It is not you. The shelf really is moving

Shrinkflation is simple enough: the pack gets smaller, or the product gets slightly different, while the price stays the same or creeps up. Sometimes the unit price goes up too. Sometimes it stays roughly level but the product quality changes. Either way, the customer is left doing mental gymnastics in aisle six.

The frustrating part is that it is designed to be hard to spot. A new pack design can make a smaller box look just as generous. A change from 12 rolls to 9 rolls can be hidden behind a bright 'value' label. A 'new recipe' can mean less of the expensive ingredient. None of this is illegal, and plenty of it is just normal commercial behaviour. But normal does not mean cheap.

The only number that really matters is the unit price

The unit price is the price per 100g, per kg, per litre, per sheet or per item. It is the closest thing you have to a fair comparison. Most UK supermarkets show it on shelf labels, but not always in the unit you expect, and online listings can be patchy. So it is worth knowing how to work it out yourself.

The formula is simple: price divided by quantity, then scaled to a standard unit. For food, compare per 100g or per kg. A £3.50 box of 450g cereal is about 78p per 100g. A £4 box of 500g cereal is 80p per 100g. The second box looks cheaper because the headline price is only 50p more, but the first is better value per gram.

Watch the base unit. £2 per 100g sounds cheap until you realise that is £20 per kg. A 'price per kg' label on one item and a 'price per 100g' label on another can make the comparison useless unless you convert them. If the shelf label is missing or confusing, use your phone calculator. It takes ten seconds and it is much more reliable than the bit of your brain that says 'that looks about right'.

Toilet rolls are the wild west of unit pricing

Toilet rolls are a brilliant example of why the headline price tells you almost nothing. One pack has 9 rolls, another has 12. One roll has 160 sheets, another has 200. One is 'quilted', one is 'recycled', one is 'extra long'. The only fair comparison is price per 100 sheets.

Say a 9-roll Pack A has 200 sheets per roll, so 1,800 sheets in total. At £8, that is about 44p per 100 sheets. A 12-roll Pack B has 160 sheets per roll, so 1,920 sheets. At £9, that is about 47p per 100 sheets. Pack B looks like better value because you get more rolls, but Pack A is cheaper per sheet. That is the kind of quiet difference that adds up over a year.

The same logic applies to kitchen roll, nappies, dishwasher tablets, bin bags and pet food. Compare the thing you actually use, not the thing the packaging wants you to count.

A special offer is a label, not a gift

Special-offer labels are not automatically bad, but they are not your friend either. 'Was £5, now £4' only tells you something if you know the unit price before and after. Sometimes the 'was' price was inflated for weeks beforehand. Sometimes the pack has shrunk at the same time. Sometimes a multibuy works out more expensive per 100g than buying one pack.

Loyalty prices deserve the same suspicion. A Clubcard price or Nectar price can be genuinely lower, but it can also be a way to make a mediocre unit price feel like a win. Check the unit price, not the coloured label. If the unit price is still poor, walk on. You are not being disloyal to a supermarket by refusing to pay over the odds.

Run a 20-minute receipt audit

You do not need a spreadsheet with 47 tabs. You need two weeks of receipts and a pen. Keep the receipts from your main shop, or take a photo of them before they go in the bin. Then pick ten staples you buy regularly: milk, bread, cereal, pasta, rice, toilet rolls, washing-up liquid, frozen peas, chicken, whatever fills your basket.

For each one, write down the pack size, the price and the unit price. If the unit price is not on the receipt, calculate it. Then compare the same item across two shops or two weeks. You are looking for three things: the same price with a smaller pack, a 'special offer' that is worse per unit than the normal version, and a pack size that has changed without the price moving.

You will probably find one or two items where the value has quietly drained away. That is your shortlist. You do not need to switch every item in your shop. Just switch the ones where the gap is big enough to matter. Ten minutes of arithmetic can easily save a few pounds a week, and that is before you count the stuff you stop buying out of habit.

Habits that stick better than willpower

Take a photo of shelf labels for your regular items. That way you have a record of the unit price when you are comparing later. Buy the bigger pack only when the unit price is genuinely lower and you will actually use it. Check drained weight on tins and jars, because the liquid is not the product. And do not assume the budget range is always cheapest; sometimes it is, sometimes it is not, and the unit price will tell you.

The point is not to become the person who argues with a shelf stacker over a 10g difference. The point is to stop paying for packaging theatre. Shrinking packs are a design choice by manufacturers, not a moral failing on your part. Your defence is boring and effective: unit price, receipt audit, repeat.

In 2026, the weekly shop is still one of the hardest bits of household budgeting to control. You cannot set the price of cereal or toilet rolls. But you can refuse to be fooled by the label. And when the packet gets smaller and the price does not, that is worth knowing.