Pack size and unit price: compare like for like across apps

Why the shelf price misleads

Two packs of the same product rarely hold the same amount. One app lists a 500 g pack, another a 1 kg pack, and a third a multipack of three small ones. Their shelf prices cannot be set side by side, because each buys a different amount.

Unit price fixes that. It turns every pack into the price of one kg, one litre or one piece, so a shopper, a category manager and a pricing team are all looking at the same thing. A pack that looks dear on the shelf can be the lower price per kg, and a pack that looks like a deal can cost more for each gram.

The method is simple arithmetic. The care is in what goes into it: the right price, the whole pack, and two readings taken under the same conditions. Each of the three rules below protects one of those.

The 3 rules for a like-for-like unit price

1. Divide the selling price by the whole pack, in one base unit

Take the selling price the app shows at that pin code, not the MRP, and divide it by the pack size. Turn the size into one base unit first: grams into kg, millilitres into litres, and counted items into pieces. For a multipack, multiply the size of one item by the count, so three 200 g items make 600 g.

Read the size from the listing, and check that the title, the size field and the pack picture agree. A pack listed as 1 kg in the title and 500 g in its details gives two unit prices, and only one of them is right. When the size cannot be read, leave the pack out rather than guess it.

2. Compare only like units

Per kg goes with per kg, per litre with per litre, and per piece with per piece. A kg and a litre measure different things, so a price per kg and a price per litre never compare, even for products that sit side by side on the shelf.

Pieces need extra care. Six eggs and twelve eggs compare well per piece, but ten small biscuits and ten large ones do not. When pieces differ in size, compare by weight instead if the listing states it.

3. Same pin code, same day, and no gaps filled in

Selling prices change with the pin code, the app and the day, so compare two readings only when they share all three. A unit price from one area on Monday against another area on Friday mixes a price gap with a place gap and a time gap.

A pack with no price that day, because it was out of stock or not checked, has no unit price. Leave it out, and never carry an older price forward to fill the gap. The difference between not checked and not available is set out in its own guide.

A worked SAMPLE

The table below is SAMPLE: invented packs and invented prices, built to show the method. It is not a reading of any app, brand or pin code.

Read the last column, not the third. The 1 kg pack has the lowest price per kg here, at ₹110. The largest pack is not the lowest per kg, and the multipack, which has the lowest shelf price after the smallest pack, costs the most for each kg.

That is the pattern unit price exists to catch. Rank the packs by price per kg, then ask why the order is what it is: an offer on one size, a premium on another, or a size listed wrongly.

When the listing already shows a unit price

Some listings print a unit price under the selling price, often per 100 g or per 100 ml. It is a useful check, but do not compare it with your own figure until you know three things about it.

1. The base it uses. Per 100 g is one tenth of per kg. Two listings that show a unit price on different bases look far apart when they are close, so turn both into per kg first.
2. The price it starts from. A printed unit price can be worked out from the MRP rather than the price you pay that day. Recompute it from the selling price, as rule 1 says.
3. The pack it counts. A multipack can show the unit price of one item, not of the whole pack. If the figure looks too low, check the count.

When your own figure and the printed one disagree, trust the one you can trace back to a price and a size you read yourself. Note the gap: a printed figure that is often wrong for one listing is worth raising with whoever manages that listing.

Set up a comparison you can repeat

A single comparison answers today’s question. A comparison you repeat each week shows how the gap between pack sizes moves, which is what a pricing or category team usually needs. Keeping it the same from one week to the next matters more than how many products it covers.

1. Fix the list. Write down the products, the pack sizes and the pin codes before you start, and keep them the same each time.
2. Fix the time. Read every pack at about the same time of day, because offers and stock can change through the day.
3. Record the inputs, not only the answer. Keep the selling price, the stated size, the count and the time for each reading, so anyone can check the figure later.
4. Mark the gaps. A pack that was out of stock or not read that day gets a blank, never a copied price from the week before.

With those four habits, a change in the ranking means the prices changed, not the method. That is the point at which a gap is worth taking to a buyer or a brand team.

Unit price as data

Rewalto’s Price per unit dataset gives this figure for each product reading. Its current status and freshness are on the commerce data page.

The dataset stores each figure per gram, millilitre or piece, by app, pin code and day. Multiply a per gram figure by 1,000 for a price per kg, and a per millilitre figure by 1,000 for a price per litre.

Read it through the API, the command line, or an AI agent over MCP (preview). Browsing the catalogue is free and every account gets 1,000 free credits a month; only delivered data uses credits.

Common traps

• Extra free offers. A pack sold with extra grams free holds more than its usual size. Use the amount in the pack you get, as the listing states it.
• Different units on one shelf. One listing gives grams and another gives kg. Turn both into kg before you divide.
• Combo packs. A pack of two different products has no single unit price. Compare it only with the same combo.
• Rounding. Round only the final figure, never the pack size, or small packs drift the most.

What unit price cannot tell you

Unit price says what one kg, litre or piece costs on the shelf. It does not say whether the product is the same quality, what the delivery fee adds, or which offers apply at checkout.

It also says nothing about the gap to MRP. That is discount depth, a separate measure with its own method. Use unit price to find the pack that buys the most for the money, and the other measures to explain why.

Nor does it say how many shoppers can buy a pack. A low price per kg on a pack that is often out of stock, or listed at only a few pin codes, helps fewer people than its figure suggests. Read unit price beside stock and coverage before you act on it.

Related reading

• Same product, different price: compare shopping apps fairly.
• Price consistency across dark stores: one product, many prices on one app.
• Discount depth: the gap between selling price and MRP.
• Coffee unit prices on the shelf.
• Commerce data: prices and stock by pin code.

Questions people ask