Unit Price Calculator
This free unit price calculator shows what each pack costs per kg, per litre or per item (per oz or lb if every pack is in ounces or pounds), and which size is the best value. You can mix grams, kilograms, ounces and pounds, or millilitres and litres.
How unit prices work
A unit price is the price of a pack divided by the amount in it, so you can see which size gives you more for your money. Since 6 April 2026, the price marking rules in England, Scotland and Wales set unit prices for food and drink per kilogram, per litre or per item. The calculator does the same: packs in grams and kilograms are shown per kg, and packs in millilitres and litres per litre. Packs in ounces and pounds (lb) are shown per oz or per lb, or per kg when you mix them with grams or kilograms.
Rules checked on 26 September 2026. Source: the government's Price Marking Order guidance on GOV.UK.
Worked example: two bags of pasta
Say a 500 g bag of pasta costs £1.10 and a 1 kg bag costs £2.40. These are made-up prices to show the sums, and the calculator opens with them filled in.
- 500 g bag: £1.10 ÷ 0.5 kg = £2.20 per kg (22p per 100 g)
- 1 kg bag: £2.40 ÷ 1 kg = £2.40 per kg (24p per 100 g)
- The 500 g bag is 20p per kg cheaper, so two of them give you 1 kg for £2.20 instead of £2.40.
How to use the unit price calculator
- Enter the price of the first pack.
- Enter its size and pick the unit: g, kg, ml, L, oz, lb or count.
- Do the same for the second pack. Press Add Item to Compare for more packs.
- Read the unit price under each pack. The cheapest has a trophy and is named as the Best Deal. If two or more packs share the lowest unit price, it says Same price instead.
Frequently asked questions
How do I work out the price per kg?
Divide the price by the weight in kilograms. For a pack in grams, divide the price by the grams, then multiply by 1,000. A 500 g bag for £1.10 is £1.10 ÷ 500 × 1,000 = £2.20 per kg.
How do I work out the price per 100 g?
Divide the price per kg by 10, so £2.20 per kg is 22p per 100 g. Before 6 April 2026, shelf labels in England, Scotland and Wales gave some foods, such as biscuits, coffee and crisps, a price per 100 g. Since then, the rules set unit prices for food and drink per kilogram, per litre or per item.
Can I compare grams with ounces, or millilitres with litres?
Yes. The calculator turns every weight into grams and every volume into millilitres before comparing, using 1 lb = 453.59237 g and 1 oz = 1/16 lb. It cannot compare a weight with a volume, such as flour in kilograms with milk in litres, so it shows a message instead of a best deal.
How do I compare multipacks, such as six cans?
Enter the total amount in the pack. Six 330 ml cans hold 6 × 330 = 1,980 ml. Or choose count as the unit and enter 6 to see the price per can.
Is the bigger pack always cheaper?
Not always. A 500 g bag at £1.10 works out at £2.20 per kg, which beats a 1 kg bag at £2.40 per kg. Check the unit price each time.
Related tools
Working out a sale price? Try the Discount Calculator. The Percentage Calculator shows how much a price has gone up or down, and the Unit Converter turns ounces and pounds into grams. Or browse all financial tools.