Unit Price Calculator
Compare supermarket prices per unit to find the best deal. Add up to 6 products with different sizes and units — instantly see price per 100g, per litre, and which is best value.
Compare unit prices across products
Enter product name, price, quantity and unit to find the best value.
Products
Why Pack Size Beats Sticker Price
Supermarket pricing is designed to obscure value. A 250g jar of coffee at £4.50 looks pricier than a 100g jar at £2.50, but the price per gram is 1.8p vs 2.5p - the bigger jar is 28% cheaper per cup. The Unit Price Calculator compares up to six products at once and ranks them by price per unit, factoring in unit conversions automatically (1 kg becomes 1,000g, 1 litre becomes 1,000ml).
Per-unit thinking exposes the so-called "family pack premium" lie that has crept into UK supermarkets since 2022. Roughly one in four "big" packs is now actually more expensive per gram than the standard size. Ariel washing pods, Heinz beans, branded breakfast cereals: a 2025 Which? survey found over 30% of multi-buys cost more per unit than the smaller version of the same product.
Where Unit Pricing Matters Most
The biggest savings come on items you buy regularly: cleaning products, pasta, rice, tinned tomatoes, cooking oil, washing detergent. A household saving 15p per kilo on rice eaten weekly saves about £8 a year, which sounds trivial until you stack it across thirty staples - that is £240 over a year of grocery shopping with zero quality compromise.
The tool also catches "unit price labelling errors". Supermarkets are legally required to display unit prices under the Price Marking Order 2004, but these tags frequently use inconsistent units (price per 100g on one product, price per kg on the neighbouring rival). Punching both into the calculator with the same unit settles it cleanly. For VAT-inclusive comparisons see the [VAT Calculator](/vat-calculator) and for percentage discount stacking try the [Discount Calculator](/discount-calculator).
Frequently Asked Questions
Is the bigger pack always cheaper?
No. About 30% of "value" or "family" packs in major UK supermarkets are now more expensive per gram than the standard size. Always check the unit price tag on the shelf edge. The reasons vary: brand strategy, supplier contracts, or simple price markup on the larger format because consumers assume it's better value.
How do I compare items sold by count vs by weight?
The tool supports an "each" or "pack" unit for items priced per item rather than weight (eggs, toilet rolls, dishwasher tablets). For a true value comparison in those categories, look at the secondary unit too: price per egg, price per sheet of toilet paper, price per wash. Some supermarkets show this on the shelf tag.
Do supermarkets have to show unit prices?
Yes. The Price Marking Order 2004 requires unit prices on most pre-packaged food, drink and household goods sold in the UK. Common units include per 100g, per kg, per 100ml and per litre. Compliance is patchy on small or own-brand items and on multi-buy promotions where the unit price often reflects the multi-buy total rather than the per-unit cost.
Why does the calculator show price to four decimal places?
Per-unit prices on cheap items can be tiny - a kilo of rice at £1.20 works out at 0.0012p per gram. Two decimal places would round most of those values to 0.00, removing the visible difference between products. Four decimal places preserves the comparison even on items priced fractions of a penny per gram or millilitre.
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