The working behind the answer
How to use this calculator
Enter the price and quantity of both packs, then choose compatible units. Weight, volume and item-count comparisons are separate modes. Use the total contents of a multipack rather than the size of one item. Both prices must be in the same currency.
The formula
Compare by weight
Unit price = pack price ÷ quantity converted to kilograms
Compare by volume
Unit price = pack price ÷ quantity converted to litres
Compare by item
Unit price = pack price ÷ item count
A worked example
Pack A costs £2 for 500g, or £4 per kg. Pack B costs £3 for 1kg, or £3 per kg. Pack B’s unit price is 25% lower than Pack A’s.
Good to know
The better-value label uses the unrounded unit prices. A difference can be smaller than the displayed monetary precision. This is a price comparison, not a recommendation about quality, shelf life or whether you will use the whole pack.
Common questions
Can I compare grams with kilograms?
Yes. In weight mode, each quantity is converted to kilograms before comparing prices.
Can I compare grams with millilitres?
No. Weight and volume need a substance-specific density to be compared. Choose the appropriate mode.