Unit Pricing: The Only Honest Way to Compare Grocery Prices

Shelf prices tell you what the package costs; unit prices tell you what the food costs to compare.

A cereal shelf can show one box priced per 100 g and the next priced per kilogram. Until you put them on the same scale, you are not comparing prices. You are comparing packaging.

Unit pricing fixes that. It turns different package sizes into one comparable number, so you can see whether the larger tub, family box, or multibuy is actually better value.

The method is simple. The useful part is knowing when the shelf tag is incomplete, when a bigger package stops being cheaper, and when a promotion only looks like a deal.

What unit pricing actually tells you

The large number on a shelf tag tells you the price of the package. The smaller unit price tells you the cost of a standard amount of the product.

That standard amount might be:

• Per 100 g for dry foods, snacks, cheese, meat, and other products sold by weight.
• Per kilogram for larger quantities of food sold by weight.
• Per 100 mL or per litre for liquids.
• Per item for products where weight or volume is not the useful comparison.

The exact unit matters less than consistency. Two products can be compared honestly only when their unit prices use the same base.

A package price answers, “What will I pay at the till?” A unit price answers, “How much product am I getting for that money?” Both numbers matter. They answer different questions.

Why shelf tags often do not line up

Retailers do not always print unit prices using the same measurement on every tag. One item may show a price per 100 g while another shows a price per kg. A liquid may be listed per 100 mL beside another product listed per litre.

This can make the numbers look wildly different even when the products are reasonably close in value. The problem is not necessarily the food. It is the measuring stick.

Unit pricing is required by law in Quebec, but it is voluntary in most of Canada. That helps explain why shelf tags can be inconsistent from one province, retailer, or store department to another. Some stores show a clear unit price. Some show it in small print. Some do not show one at all.

Rules and display practices can also vary by product type and location. Treat the shelf tag as helpful information, not a guarantee that every comparison has already been done for you.

If a unit price is missing, unclear, or based on a different unit, do the conversion yourself.

The basic unit-price formula

Use this formula:

Unit price = package price ÷ package quantity × comparison unit

The comparison unit is the amount you want to use for every product. For many grocery comparisons, per 100 g is practical. For liquids, per 100 mL often works well.

For example, if a package contains 750 g, convert the package quantity into 100 g portions:

• 750 g ÷ 100 g = 7.5 portions.
• Divide the package price by 7.5.
• The result is the price per 100 g.

You do not need to do this for every item in the aisle. Compare the products that are genuinely interchangeable, then check whether the better unit price fits your household’s needs.

How to normalise different shelf units

If one tag uses kilograms and another uses 100 g, convert one of them before comparing.

There are 1,000 g in a kilogram. That means:

• To convert a price per kilogram to a price per 100 g, divide by 10.
• To convert a price per 100 g to a price per kilogram, multiply by 10.

The same idea works with liquid measurements:

• There are 1,000 mL in a litre.
• To convert a price per litre to a price per 100 mL, divide by 10.
• To convert a price per 100 mL to a price per litre, multiply by 10.

Write the units beside the numbers while you calculate. That small habit prevents one of the most common mistakes: comparing a per-kilogram figure directly with a per-100-gram figure.

When you are in a hurry, choose one standard and convert everything to it. Do not switch back and forth halfway through the comparison.

When a bigger package is actually cheaper

A larger package is cheaper only when its unit price is lower. The total package price does not decide this.

A bigger container can cost more at the till and still be better value because it contains more food for each dollar. It can also cost more and be worse value if the price per 100 g, 100 mL, or item is higher.

Use this quick test:

1. Find the total quantity in each package.
2. Put both quantities into the same unit.
3. Divide each package price by its quantity.
4. Multiply both results to the same comparison unit.
5. Choose the lower unit price only if you will use the product before it spoils or loses quality.

This last point matters. A lower unit price is not a saving if half the food ends up in the bin. The best package is the one with a good unit price that your household can realistically finish.

For fresh foods, consider shelf life, storage space, freezer space, and how often your family eats the item. For pantry foods, check the best-before date and whether you already have several packages at home.

How multibuys hide the real comparison

“Two for” offers and family packs make the total price look important. It is not enough to know what the bundle costs. You need to know how much product the bundle contains.

First, add the quantities together. Then divide the total multibuy price by the total quantity. Compare that result with the regular package’s unit price.

Do not assume a multibuy is cheaper because:

• The sign uses bold promotional wording.
• The bundle contains more than one package.
• The total price looks lower than buying several single items.
• The package is labelled family size.
• You were planning to buy the product anyway.

A multibuy can be useful when the combined unit price is lower and you will use everything. It may not be a deal when the bundle is priced around the same unit cost as individual packages, or when the promotion encourages you to buy more than planned.

Also check the terms before deciding. A multibuy may require a specific quantity, mix of products, loyalty account, or other condition. Store rules change, so read the current sign and check the receipt if the deal matters to your budget.

Unit pricing is not a complete nutrition comparison

Unit price tells you how much the product costs. It does not tell you whether two products are equivalent.

Compare like with like where possible. A block of cheese and a processed cheese product may have different ingredients and uses. A jarred pasta sauce may contain different amounts of vegetables, oil, or added sugar. A larger bag of frozen food may include more unusable pieces or a different mix.

For packaged foods, check the net quantity rather than the number of servings printed on the front. Serving sizes can differ between brands. Also check whether the package includes liquid, glaze, or brine when that affects what you will actually eat.

Unit pricing is a starting point for value, not permission to ignore quality, ingredients, dietary needs, or waste.

A fast unit-price routine for the shop

Use the same routine each time:

1. Pick the products you would genuinely substitute for one another.
2. Check the unit printed on each shelf tag.
3. Convert them to one unit if the tags do not match.
4. Compare the lowest unit price.
5. Check the total quantity, expiry or best-before date, and storage needs.
6. Recheck multibuys using the combined quantity.
7. Buy the package your household will actually use.

If the shelf tag is missing, use your phone calculator. Enter the package price, divide by the package quantity, and multiply to your chosen comparison unit. Keep the measurement visible in your notes so you do not accidentally compare grams with kilograms.

This is especially useful when comparing prices across different stores. Flyers and online listings do not always display measurements in the same way either. A per-100-g comparison can make a product at No Frills, FreshCo, Metro, IGA, Costco, or a local independent grocer easier to assess without relying on the biggest sale label.

Store selection and prices vary across Canada, including between provinces, cities, smaller communities, and northern areas. Unit pricing gives you a consistent method even when the stores and package sizes change.

Make unit pricing part of your weekly plan

The goal is not to choose the cheapest package blindly. It is to spend your grocery budget on the food you need, in quantities your household can use, without being distracted by packaging or promotional language.

Once you compare unit prices, you can build a shopping list around the better-value options available at your chosen stores and keep the total within your budget. CartBrain can help with the wider weekly plan, while the unit-price check keeps your package decisions honest at the shelf.