PACK SIZE
Bigger is usually cheaper
In the CMA basket, unit prices generally fell as packs got bigger, but toilet roll, cheese and laundry pods had examples where bigger cost more per unit.
Check a pack sizeStart
WHAT THE CMA FOUND
Read the
small number.
The best value is per kilo, not per pack.
Under the Price Marking Order, most shops must show a unit price: the cost per kilogram, litre or item. The Competition and Markets Authority found it often beats the shortcuts shoppers rely on.
PER KGper litre, per item
Check a pack sizeKeep in mind
- Bigger is usually cheaper, not always
- Offers are not always best value
- Loose can beat bagged
- One number to compare like with like
THE SHORT ANSWER
Check the unit price,
not the pack.
Shoppers often use rules of thumb.
The CMA tested them on 26 everyday groceries.
OFFERS
A deal is not always the best deal
Promoted items often had the lowest unit price, but the CMA found ketchup and laundry detergent offers that cost the same or more per unit than other sizes.
See the numbers
LOOSE
Loose or bagged?
The CMA’s short guide says pre-packed bags of fruit and veg aren’t always cheaper than loose. The unit price lets you compare.
How to use itGeneral information only, not financial advice. For advice on your own situation, speak to a regulated financial adviser or a free money-advice service.
A QUICK PACK CHECK
How much does
sizing up save?
Pick a product from the CMA’s basket to see how much the unit price fell in bigger packs. The bar shows the size of the saving per unit.
Averages from the CMA’s 2024 analysis of a basket of 26 grocery products. Prices change over time and between shops, so check the label.
TWO NUMBERS WORTH KNOWING
The same food,
very different prices.
How much the unit price can move with pack size,
and how big a shop has to be to show it.
≈ 60% cheaper
4 pints vs 1 pint, per unit
In the CMA’s basket, the unit price of a 4-pint bottle of milk was almost 60% cheaper than a 1-pint bottle. For washing-up liquid the saving from the biggest pack was about 5%.
MILK · CMA 2024
280 m²
Floor area below which pre-packs are exempt
Shops with a relevant floor area of 280 square metres or less do not have to unit price goods pre-packed in constant quantities.
SMALL SHOPS · PMO
From 6 April 2026, amendments to the Price Marking Order mean loyalty prices must be shown with their own unit price, alongside the normal price, according to government guidance.
FOUR HABITS TO TRY
Compare like
with like.
The unit price is usually next to or below the selling price, often in smaller print. These habits come from the CMA’s short guide for shoppers.
Step 1
Find the small print
Look next to or below the main price on the shelf label, or under the price online.
Step 2
Check the units match
Per 100g and per kg, or per kg and per item, cannot be compared directly. The CMA found this put shoppers off.
Step 3
Test the offer
Compare a promotion’s unit price with other sizes; offers and multipacks are not always cheaper per unit.
Step 4
Re-check old favourites
Unit prices can change over time and between shops, so check them even on the items you always buy.
THE RULES
Why the label
shows it.
The Price Marking Order 2004 requires most traders to show a selling price and a unit price. Government guidance gives the example of two £3 cereals: a 500g box is £6 per kilogram, a 2kg box is £1.50.
In 2023 the CMA found inconsistencies, such as mayonnaise priced by weight in one place and by volume in another, and recommended reform. The amended rules, in force from 6 April 2026, require prices to be clearly legible and cover loyalty prices.
Questions
Questions on the way
What is a unit price?
It is the price for a standard measure, such as per kilogram, per litre or per item. It lets you compare products of different sizes on a like-for-like basis.
Is the bigger pack always better value?
Usually but not always. In the CMA’s basket of 26 products, unit prices generally fell with pack size, but toilet roll, cheese and laundry pods had examples where larger packs cost more per unit.
Are special offers always the cheapest option?
No. The CMA found promoted products often had the lowest unit price, but also examples, such as ketchup and laundry detergent, where an offer cost the same or more per unit than another size.
Why do some small shops not show unit prices?
Under the Price Marking Order, shops with a relevant floor area of 280 square metres or less do not have to unit price products pre-packed in constant quantities.
What changed in April 2026?
Government guidance says amendments to the Price Marking Order came into effect on 6 April 2026. Loyalty prices now need their own unit price, and prices must be clearly legible and unambiguous.
Destination