Unit Pricing: The Supermarket Label That Tells You the Real Price

The big number on a supermarket shelf label is the price of the pack. It is not the price of the food. Two packets of rice can carry very different sticker prices and turn out to cost almost exactly the same per kilogram — or a smaller, apparently more expensive pack can be cheaper per kilogram than a "family size" bag next to it. The figure that tells you which is genuinely better value is the unit price, usually printed in smaller type on the same label.

Learning to read it takes a few minutes. Using it consistently can save a noticeable amount every week, because it cuts through pack sizes, offers and branding to show you what you are really paying.

What a unit price is

A unit price is the price of a product expressed per standard unit of measurement. Depending on the product and the country, that might be:

• per kilogram or per 100 grams for dry and solid foods;
• per litre or per 100 millilitres for liquids;
• per item, per sheet, per wash or per 100 sheets for things like eggs, kitchen roll, toilet paper and laundry detergent.

In many countries, larger retailers are required or encouraged to display unit prices on shelf labels and in online listings. The format differs from shop to shop, but the idea is the same: it lets you compare products of different sizes on equal terms.

Why the pack price misleads

Pack prices make comparison hard for several reasons:

• Pack sizes vary. A 400 g packet and a 1 kg packet cannot be compared by their sticker prices alone.
• Packs shrink. Manufacturers sometimes reduce the contents of a product while keeping the price and packaging similar — often called "shrinkflation". The pack price looks unchanged; the unit price reveals the increase.
• Promotions focus on the pack. "Now only 2.00!" says nothing about whether the deal beats the larger pack on the shelf below.
• Bigger is not always cheaper. It is a common assumption that larger packs are always better value, but this is not guaranteed. Sometimes a mid-sized pack, or two small ones on offer, has a lower unit price than the largest size.

How to read a shelf label

A typical shelf label shows:

1. The product name and size (for example "Long grain rice 1kg").
2. The selling price in large type.
3. The unit price in smaller type (for example "0.18 per 100g" or "1.80 per kg").

When comparing products, make sure you compare like with like. One label might show the price per kilogram and another the price per 100 grams. Multiply the per-100-gram figure by ten to convert it to per kilogram. Where a label is missing or unclear, you can work it out yourself.

Working out a unit price yourself

The calculation is simple:

Unit price = pack price ÷ quantity in the pack

For example:

In this illustration the 5 kg bag is the cheapest per kilogram. Whether it is the best buy depends on whether your household will use five kilograms of rice before it goes stale or attracts pests — which brings us to the limits of unit pricing.

The prices in the table are invented to show the method. Real prices vary by country, shop and season.

When the lowest unit price is not the best buy

Unit pricing tells you the cost per kilogram. It does not tell you:

• Whether you will use it all. A large bag of salad leaves at a lower price per kilogram is a loss if half of it wilts. For perishable food, buy the quantity you will actually eat.
• Whether you have room to store it. Bulk packs need cupboard or freezer space, and stored food needs protecting from damp and pests.
• Whether quality differs. Two products with the same unit price might differ in taste, texture or ingredients. For some items, a slightly higher unit price for a product your household prefers is worth it, because the cheaper one would go uneaten.
• Whether you can afford the outlay. Bulk buying requires more money up front. If your budget is tight this week, the cheaper pack price may matter more than the lower unit price, and that is a reasonable choice.

Unit pricing is a tool for comparison, not a rule that the cheapest unit price always wins.

Using unit prices on offers

Promotions are where unit pricing earns its keep.

• Multi-buys. "3 for 2" sounds generous, but check the unit price of the deal against the larger single pack. Sometimes the big pack is still cheaper.
• Percentage-off deals. A discount on a small premium product can still leave it more expensive per kilogram than the regular price of a standard product.
• Loyalty prices. Some shops show a lower price only for members. Compare the member unit price, if that is the price you will pay.
• "Bigger pack, same price" offers. These can be genuine value — the unit price will show it immediately.

Unit prices beyond food

Unit pricing is just as useful for household products, where pack sizes and concentrations vary wildly.

• Laundry detergent: compare price per wash rather than per litre, because concentrated products need smaller doses. Check the dosing instructions to see how many washes a pack really provides at your water hardness and load size.
• Toilet paper and kitchen roll: compare price per 100 sheets, and note that sheet sizes and ply differ, so a "mega roll" may not contain as much as it seems.
• Dishwasher tablets: price per tablet.
• Nappies and wipes: price per item.
• Pet food: price per kilogram, considering also the recommended daily amount, since denser foods may need smaller portions.

Online shopping

Online grocery listings usually display unit prices next to each product, and many shops allow you to sort search results by price per kilogram or per litre. This is one of the easiest ways to find the best value in a category: search for "chopped tomatoes", sort by unit price, and the cheapest options rise to the top.

Be aware that substitutions in online orders may change the unit price, and that delivery charges and minimum order values add to the total cost of the basket.

Building the habit

At first, checking unit prices slows you down. After a few weeks, you start to remember the typical unit price of the items you buy most often, and comparison becomes almost automatic. A few ways to make it easier:

• Focus on your top twenty items. Most of a weekly shop is made up of the same products. Learn their usual unit prices and you will spot a good deal — or a stealth price rise — immediately.
• Keep a price note. A simple list on your phone of your regular items and their usual unit price at different shops shows you where each is cheapest.
• Check the shelves above and below. The products at eye level are not always the cheapest per unit.
• Watch for pack changes. If a familiar product's packaging changes, check whether the weight has changed too.

A worked example from a weekly shop

Imagine a household buying pasta, tinned tomatoes, oats and laundry detergent. Without unit prices, they pick the brands they always buy in the sizes they always buy. With unit prices, they notice:

• The own-brand pasta in a 1 kg bag costs noticeably less per kilogram than the branded 500 g pack.
• Four-tin multipacks of tomatoes are no cheaper per kilogram than single tins, so they buy singles as needed.
• A large bag of plain oats costs far less per kilogram than the small boxes of "instant" oats, which are essentially the same food rolled thinner.
• A concentrated detergent that looked expensive works out cheaper per wash than their usual brand.

None of these switches involves eating less or compromising on quality. They simply move spending to the same products in better-value formats.

Common unit-pricing traps

Even careful shoppers get caught out occasionally. Watch for these situations:

• Different units on neighbouring labels. One product shows a price per kilogram, the next a price per 100 grams or per item. Convert them to the same unit before comparing.
• Drained weight versus total weight. Tinned vegetables, fish and fruit may list both. The drained weight — the food without the liquid — is the more useful figure when comparing value.
• Multipacks with mixed sizes. A multipack of yoghurts or crisps may contain smaller portions than the individual items on the same shelf.
• Labels that were not updated. Shelf labels occasionally lag behind price changes. If something looks wrong, check the price at the till or in the online listing.
• Concentrated versus ready-to-use. Squash, cleaning sprays and detergents may be concentrated. Compare the cost of the amount you will actually use, not the cost per litre of liquid in the bottle.

Teaching children unit pricing

Unit pricing is a useful practical maths lesson. Older children can be asked to find the cheapest cereal per 100 grams or the best-value bag of apples, which turns the weekly shop into a game and teaches a skill they will use for life. It also helps them understand why the family chooses one product over another, which can reduce requests for the most heavily advertised items.

The bottom line

The unit price is the honest price. It strips away pack sizes, promotional language and branding and lets you compare what you are actually paying for. Use it to choose between brands and sizes, to judge offers, and to notice when products quietly shrink. Combine it with common sense about storage, waste and household preferences, and it becomes one of the simplest, most reliable ways to lower your grocery bill without changing what you eat.