Unit Price Calculator: Compare Grocery Sizes and Deals

Price per kilo and the real discount of a multi-buy offer

Price per kilo equals total price paid ÷ total quantity in kg (or litres). A “second one half price” offer only cuts the price per kilo by 25% across two items, and a “buy 2 get 1 free” bundle by 33.3%. The tool ranks up to six products by unit price after the offer.

What the tool calculates

• Price paid after the offer: straight discount = price × (1 − discount); “second at −X%” = odd items at full price, every second item discounted; “buy 2 get 1 free” = you pay for 2 items in each group of 3, leftover items at full price.
• Quantity converted to kg, litres or pieces (1 oz = 28.3495 g, 1 lb = 453.592 g), then unit price = price paid ÷ quantity. The tool also shows the price per 100 g or 100 cl, except for items sold by the piece.
• Only items of the same kind as the first one (weight, volume or pieces) are ranked: the cheapest per unit wins, the others show how much dearer they are in %, and “max savings” compares the dearest with the cheapest. An item of another kind is marked “not compared”.

Worked example

Standard 500 g pack at 2.80: 5.60/kg. Three identical packs on “buy 2 get 1 free”: 5.60 for 1.5 kg, so 3.73/kg. Family pack of 1.2 kg at 6.90: 5.75/kg. The bundle wins; the standard pack is 50% dearer per kilo, the family pack 54%, and maximum savings reach 35%. Two packs on “second half price” cost 4.20 for 1 kg (−25%); three packs cost 7.00 for 1.5 kg (4.67/kg), because the third is full price.

Limits

• Prices per kilo, per litre and per piece cannot be compared: change the first item’s unit to rank another group.
• “Buy 2 get 1 free” is fixed (no “3 + 1”) and offers cannot be stacked.
• Unit price says nothing about quality or drained weight, which the legal label uses for tinned food.

Sources and dates: in France, unit pricing per kilo or litre of pre-packed goods is required by the order of 16 November 1999; an advertised price cut must be based on the lowest price of the previous 30 days (French Consumer Code, art. L112-1-1, in force since 28/05/2022, transposing Directive (EU) 2019/2161); a smaller pack with a higher unit price must be flagged for two months (order of 16 April 2024, in force 01/07/2024) (checked 14/10/2026).

Frequently Asked Questions

How do I work out the price per kilo?

Divide the price paid by the weight in kilograms. A 500 g pack at 2.80 costs 2.80 ÷ 0.5 = 5.60 per kg; for grams, divide by the weight and multiply by 1,000.

What is the real discount on “second one half price”?

For two items you pay 1.5 times the price instead of 2, so the real discount is 25%. With “second one 70% off” it rises to 35%, but only if you actually buy two.

How much does “buy 2 get 1 free” save?

You pay for 2 items and get 3, so the unit price falls by 33.3%. Three 500 g packs at 2.80 work out at 3.73 per kg instead of 5.60 per kg.

Is the bigger pack always cheaper?

No. A 1.2 kg family pack at 6.90 costs 5.75 per kg, more than a 500 g pack at 2.80 (5.60 per kg). Always compare the price per kilo or litre shown on the shelf label.

What price must an advertised discount be based on?

In France, since 28 May 2022, the reference price for an advertised reduction is the lowest price the shop charged in the previous 30 days (Consumer Code, art. L112-1-1, from EU Directive 2019/2161). A “30% off” worked out from a price raised just before the offer does not comply.

Is this tool really free?

Yes, all tools on Kristools are 100% free and accessible without registration.

Is my data protected?

Yes. All processing is performed directly and securely inside your browser. No personal data is sent to our servers.