To compare grocery packs fairly, divide the price you will actually pay by the total quantity, then compare both products in the same unit. A larger pack can cost less per kilogram while costing more at checkout; a multipack can lose its advantage once delivery is included.
Use CheckMatter’s Unit Price Comparison Calculator to compare up to four options per kilogram, litre or piece. This guide shows how to choose the inputs, interpret the result and decide whether the lowest unit price is useful for your household.
Prepared for CheckMatter under its editorial policy. Examples and calculator behaviour checked on 16 October 2026. All prices below are invented examples, not current retailer offers.
The unit price formula
Unit price = total price ÷ total quantity in the chosen unit. For a multipack, first multiply the quantity in one pack by the number of packs. Use net contents, excluding packaging.
- Price per kilogram = price ÷ grams × 1,000.
- Price per 100 g = price ÷ grams × 100.
- Price per litre = price ÷ millilitres × 1,000.
- Price per piece = price ÷ total number of comparable pieces.
For example, ₹84 for 400 g is ₹84 ÷ 400 × 1,000 = ₹210/kg, or ₹21 per 100 g. Comparing ₹21 per 100 g against ₹200/kg requires converting one figure: ₹21 per 100 g is ₹210/kg, so ₹200/kg is lower.
NIST’s unit-pricing guidance explains the use of cost per unit of measure for comparing products and recognising package downsizing. The arithmetic applies to these rupee examples; this article does not make claims about Indian labelling requirements.
Worked example: which of four grocery packs is cheapest?
Imagine four offers for the same type and quality of dry oats. Delivery is free, every pack is available, and you expect to use everything before it spoils.
| Option | Quantity | Total price | Price/kg |
|---|---|---|---|
| A: small pack | 400 g | ₹84 | ₹210 |
| B: medium pack | 750 g | ₹150 | ₹200 |
| C: large pack | 1.2 kg | ₹252 | ₹210 |
| D: multipack | 3 × 250 g = 750 g | ₹144 | ₹192 |
D has the lowest unit price. A has the smallest checkout bill, but C’s larger size offers no unit-price advantage over A. B and D contain the same total quantity, so choosing D instead of B saves ₹6 on that purchase.
Compare A and D on equal quantities: 400 g at D’s rate would cost ₹76.80, a saving of ₹7.20 against A. That is a normalised comparison, not a claim that the shop sells 400 g of D for ₹76.80. The actual multipack still costs ₹144.
How to enter these offers in the calculator
- Open the Unit Price Comparison Calculator. Leave A and B included, and enable C and D.
- For A, enter total price 84, quantity 400, packs 1, and unit Grams.
- For B, enter 150, 750, 1, and Grams. For C, enter 252, 1.2, 1, and Kilograms.
- For D, enter 144, 250, 3, and Grams. Enter the price for all three packs, not ₹48, which is the price of only one.
- Choose Calculate. D should rank first at ₹192/kg. The saving against A for A’s 400 g reference quantity is ₹7.20.
For liquids, select Millilitres or Litres for every option. For comparable count-based products, use Pieces and enter the count within each pack. Do not compare grams with millilitres unless you have a product-specific density conversion; the calculator rejects mixed dimensions.
Include offers, coupons and delivery consistently
Use the payable price after a discount you can actually claim. Do not subtract conditional future cashback that you may never receive. If you need to calculate an offer first, use the Discount Calculator.
In the oats example, suppose D alone requires ₹24 delivery while B is available without a delivery charge. D then costs ₹168 ÷ 0.75 kg = ₹224/kg. B, at ₹200/kg, becomes cheaper. The calculator includes delivery only when you add it to the entered total price.
For a shared basket delivery fee, state how you allocate it and use the same method for the alternatives. If the fee stays identical whichever pack you choose, compare the change in the whole basket’s payable total as well as the product unit price. A coupon minimum that makes you buy unwanted items can erase the apparent saving.
“Buy two, get one free” means three packs in the quantity denominator. For identical 100 g packs costing ₹32 each, the promotion costs ₹64 for 300 g: ₹213.33/kg, rounded only at the end. Compare that result with other pack sizes rather than with the headline discount alone.
Spot shrinkflation when the sticker price stays the same
Suppose an old pack cost ₹100 for 500 g and its replacement costs ₹100 for 450 g. The old unit price was ₹200/kg; the new price is about ₹222.22/kg.
The pack contains 10% less product, but the price per kilogram has risen by about 11.11%. These percentages have different denominators:
- Quantity reduction: (500 − 450) ÷ 500 × 100 = 10%.
- Unit-price increase: [(100 ÷ 450) ÷ (100 ÷ 500) − 1] × 100 ≈ 11.11%.
Keep the previous receipt or a note of the old price and net quantity. Compare equivalent products and formulations; a change in ingredients, concentration or quality may require a separate judgement. For the underlying percentage method, see our percentage increase and decrease guide.
When the lowest unit price is not the best purchase
A bulk pack saves money only if enough of it is useful to you. If you pay ₹200 for 1 kg but discard 200 g, the cost of the 800 g you use is ₹250/kg of usable product. A 500 g pack at ₹120 costs ₹240/kg and is cheaper per usable kilogram if you finish it all.
Also check available storage, expiry dates and whether the products do the same job. Concentrated detergent may require a different dose per wash; a lower price per litre alone does not settle that comparison. For products packed in liquid, distinguish net weight from drained weight where relevant and keep the basis consistent.
The UK Competition and Markets Authority’s consumer guide describes unit pricing as a way to compare pack sizes and offers, while also recognising that storage, waste and product differences matter. Its regulatory context is the UK.
Frequently asked questions
Is the largest pack always the cheapest?
No. In our example, the 1.2 kg pack and 400 g pack both cost ₹210/kg. Compare the unit prices after applying valid offers and relevant charges.
Can I compare two brands?
Yes, on a consistent quantity basis. The result compares price, not taste, ingredients, strength or quality. Decide whether those differences matter before treating the products as substitutes.
Why does the calculator’s saving differ from the difference in checkout prices?
The calculator compares the lowest rate with A’s rate for A’s quantity. Checkout totals can differ because the packs contain different amounts. When two offers contain the same quantity, the two comparisons coincide.
Can I use this for an entire shopping basket?
Compare each group of equivalent products separately. Adding the kilograms of unrelated foods or mixing litres and pieces would not produce a meaningful basket unit price. Add the final payable totals separately to check your budget.
Before buying: check net quantity, calculate all packs, use one unit, include applicable costs, and choose an amount you can use. Compare your own pack prices here.