Unit Pricing UK: Compare Grocery Packs on the Same Basis

A larger pack can look economical without actually being cheaper for the amount you receive. A bright promotion label can be equally distracting. Unit pricing UK shoppers use is a way to put different pack sizes on the same basis, so you can compare the product rather than the packaging. It is a useful calculation, but the lowest unit price still needs to fit your available cash, storage space and likely use.

Unit pricing UK: find the comparison figure

Look for the price per kilogram, litre, 100 grams or individual item on the shelf label or online listing. The selling price tells you what leaves your account; the unit price tells you the cost for a standard quantity.

The CMA's unit pricing work explains why comparing standard quantities can help shoppers assess value. Its analysis also shows that assumptions about large packs or particular packaging do not always identify the cheapest option.

Check that the label belongs to the exact product you are holding. A nearby shelf ticket can refer to another size or flavour, particularly after products have been moved.

Convert different units before comparing

You cannot compare a price per 100 grams directly with a price per kilogram. Convert one so both figures describe the same quantity.

For illustration, £0.40 per 100 grams equals £4 per kilogram. A product marked £3.60 per kilogram is cheaper on that basis, provided the products are reasonably comparable.

Use a phone calculator if needed. The goal is a dependable comparison, not mental arithmetic under pressure in the aisle. Keep the calculation simple and round only after you have identified which option costs less.

Calculate a missing unit price

Divide the pack price by its quantity, using the same measurement for both options. A hypothetical 500-gram pack costing £2 has a unit price of £4 per kilogram.

A hypothetical 750-gram pack costing £3.30 has a unit price of £4.40 per kilogram. Despite being bigger, it costs more for the same weight. These are examples rather than current supermarket prices.

For products sold by count, check the number of usable items. A six-pack and an eight-pack can be compared per item, but that comparison may not be meaningful if the individual items are very different sizes.

Compare like with like

Unit price does not explain every difference in value. Consider whether the products perform the same job, meet dietary requirements and provide the amount you need.

A concentrated cleaning product may have different dilution instructions from a ready-to-use version. A lower price per litre does not automatically mean a lower cost per cleaning task. Follow the label rather than inventing a dilution that appears cheaper.

With food, consider edible quantity and suitability. An ingredient that nobody in the household will eat is unlikely to be good value regardless of the comparison figure.

Check promotions and membership prices

Read which price the displayed unit figure uses. An offer available only with a particular membership or purchase quantity should not be compared with a price you cannot actually obtain.

Calculate the amount you would pay for the exact basket. A multi-buy can reduce the unit cost while increasing the total cash needed today. That matters when the week's food budget is limited.

Do not buy extra merely to achieve a promotional threshold. If the extra items are unnecessary, the offer can raise your overall spending even when the advertised saving is mathematically correct.

Include waste in the decision

Ask how much of the larger pack you will realistically use. A lower unit price can be outweighed by food discarded or a product that expires before you finish it.

For illustration, paying £4 for a pack and using only half gives a different practical result from paying £2.50 for a smaller pack you use completely. The shelf comparison is a starting point, not the whole decision.

Plan around appropriate storage and product instructions. Do not assume every item can be kept indefinitely or safely frozen simply because a larger quantity would reduce its listed unit cost.

Keep a short list of common purchases

For frequently bought items, record the usual pack size and recent unit price. A small list can help you notice a changed price or a smaller pack without trying to remember every product in the shop.

Update the record when you actually buy, since prices and promotions change. An old figure is useful historical context, but not a promise of what another retailer charges today.

Avoid making a special trip for a tiny price difference without considering travel cost and time. A practical shopping plan should assess the full trip, not just the cheapest individual label.

Use the method where it helps most

Start with a few products where pack sizes vary significantly, then expand the habit if it helps. You do not need to calculate every item before completing a normal shop.

Keep total spending visible throughout. The best basket combines suitable products, sensible quantities and prices you can afford today. Browse the PennyGuide UK blog for more everyday shopping guidance.

Checked 9 October 2026. Retailer prices and promotions change. Calculations are illustrative. Cover photograph: Unsplash; illustrative stock image.