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Unit Price Calculator

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Supermarket shelf labels print a unit price when they are required to, in whichever unit the shop finds convenient, and stop entirely at the market stall. This calculator does the same arithmetic for whatever is in front of you: enter each pack's price and size, and it ranks them by what a gram, a millilitre or an item really costs — then tells you what the difference adds up to.

What is being measured

Changes how the rate is displayed. It never changes which pack wins.

6 for a six-pack

6 for a six-pack

How to use the unit price calculator

  1. 1Pick whether you are comparing by weight, by volume or by count.
  2. 2Enter the price of the first pack, how many identical units are inside it, and the size of each one. A six-pack of 330 ml cans is 6 packs of 330 ml, not one pack of 1,980 ml — either works, but the first is easier to read off the label.
  3. 3Do the same for the second pack. Add up to five in total.
  4. 4Choose how you want the rate shown — per 100 g, per kilogram, per pound. This changes the display and never the ranking.
  5. 5Press Compare. The cheapest row is highlighted, and the panel underneath shows what each other pack costs you over buying the same contents at the best rate.

Examples

The big bag is not always cheaper

Input
500 g at ₹180 against 1.5 kg at ₹560
Result
The 500 g pack is ₹36.00 per 100 g; the 1.5 kg pack is ₹37.33 per 100 g

A 3.7% premium for buying more. Family packs are priced on the assumption that nobody checks, and often they are cheaper — but not reliably.

A multipack against a single bottle

Input
6 × 330 ml at ₹270 against 1 × 2 L at ₹150
Result
The multipack is ₹13.64 per 100 ml; the 2 L bottle is ₹7.50 per 100 ml

The multipack costs 82% more per millilitre. Portioning and chilling are worth something, but this is what they cost.

Across two measurement systems

Input
750 g at £4.20 against 2 lb at £5.10
Result
The 750 g pack is £0.56 per 100 g; the 2 lb pack is £0.56 per 100 g — a tie to the penny

Two pounds is 907.18 g. Comparing these by eye is guesswork, which is the case this tool is really for.

About the unit price calculator

Why bigger is not reliably cheaper

The received wisdom is that buying in bulk saves money, and often it does — larger packs spread the packaging, handling and shelf space over more product. But the price on the shelf is not a cost calculation, it is a decision by a retailer about what people will pay, and a well-documented amount of the time the larger pack carries a higher unit price than the smaller one. Sometimes that is a promotion on the small size that has not been reflected in the large; sometimes it is deliberate, because shoppers reach for the family pack without checking.

This is exactly the kind of comparison people are bad at doing in their heads, and not for lack of arithmetic. The numbers are chosen to be awkward — 340 g against 1.2 kg, 750 ml against 2 L — and the mental shortcut most of us use is to compare the total prices and the pack sizes separately, which is not the same calculation. Doing the division properly takes seconds and changes the answer more often than most people expect.

Where unit pricing is required by law, the required unit varies: one shop prints per 100 g and another per kilogram for comparable products, which is enough to defeat quick comparison. Markets, delis and most of the online grocery world do not print one at all. Where the label is missing or awkward, this is the arithmetic to do.

The three ways a comparison goes wrong

The first is the multipack. A box described as 6 × 330 ml holds 1,980 ml, and treating it as 330 ml makes it look wildly expensive while treating the whole box as one unit makes an ordinary bottle look wildly cheap. The pack count is the first thing to get right, and it is the reason this calculator asks for it separately instead of expecting you to multiply.

The second is mixed units. A price per pound and a price per kilogram cannot be compared by looking at them, and neither can US fluid ounces against imperial ones — the two differ by about 4%, and the gallons by about 20%. Converting to a single base before dividing is the only way to be sure, and it is where the arithmetic stops being something to do at the shelf.

The third is comparing things that are not the same product. Concentrated and ready-to-use versions of the same cleaner, dried and tinned pulses, ground coffee against beans — the unit price is arithmetically correct in each case and answers a question you did not ask. The tool compares the numbers you give it, and deciding that two products are genuinely substitutable is the part that stays with you.

Frequently asked questions

Does the unit I choose to display change which pack wins?
No, and it cannot. Every pack is reduced to a price per gram, millilitre or item first, and the ranking is decided on that. Showing the result per 100 g rather than per kilogram multiplies every row by the same ten, which moves the decimal point and nothing else. Pick whichever matches the shelf label you are checking against.
How do I enter a multipack?
Put the number of identical units in the packs box and the size of one unit in the size box — 6 and 330 ml for a six-pack of cans. Entering 330 ml with the price of the whole box is the mistake that makes multipacks look six times worse than they are, which is why the count is a separate field rather than something to multiply in your head.
Can I compare a 500 g pack against a 2 lb one?
Yes. Every unit inside a measurement family converts to a single base — grams for weight, millilitres for volume — so pounds, ounces, kilograms and grams mix freely, as do litres, US fluid ounces and imperial ones. What the tool refuses is a comparison across families: a price per gram and a price per millilitre are different quantities, and turning one into the other needs a density it has no way of knowing.
Why does it also show what the difference costs in money?
Because a percentage is easy to shrug at. Told that one pack is 12% dearer per kilogram, most people carry on; told that this particular trolley-load costs ₹94 more than the same food in the other size, rather fewer do. The figure shown is what that pack would have cost at the cheapest rate, and the gap between the two.
So is the cheapest per-unit price always the right buy?
Often, and not always — and the calculator knows nothing about the exceptions. A larger pack that goes off before you finish it costs more per gram actually eaten than the small one did. So does a size that will not fit the cupboard, a multibuy that needs three of something you want one of, or a bulk bag of a food you turn out not to like. Unit price is one input to the decision and this tool computes exactly that one.

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