What Is Unit Pricing? How to Compare Grocery Prices by Size

You're standing in the cereal aisle trying to decide between two boxes. One is $5.49, the other is $7.29. Obviously the first one is cheaper — but is it actually the better deal?

Not necessarily. If the $5.49 box is 400g and the $7.29 box is 700g, the math flips completely. The bigger box costs less per gram — sometimes by a surprisingly wide margin.

This is the core idea behind unit pricing: instead of comparing sticker prices, compare the cost for an equal amount of product.

What unit pricing means

Unit pricing is the cost of a product expressed in a standardized unit — typically per 100 grams, per 100 mL, or per item. It lets you compare products with different package sizes on equal terms.

For example:

• A 500g jar of peanut butter priced at $4.99 costs $0.998 per 100g
• A 750g jar of the same brand priced at $6.49 costs $0.865 per 100g

The bigger jar costs about 13% less per gram in this example.

Many Canadian shelf tags include a unit price, but the presentation is not always consistent. The font can be small, and neighbouring products may use different units. That makes a quick comparison harder than it should be.

Why "bigger is cheaper" is not always true

The most common assumption about unit pricing is that bulk packages always win. In many cases that's true — but not always, and the exceptions matter.

A few situations where the smaller package is actually the better value:

Sales on smaller sizes. Promotional pricing on a standard-sized item can temporarily make it cheaper per unit than the regular-priced bulk version. If you're not checking both, you might buy the bigger one on autopilot and pay more.

Private-label vs. name-brand. A smaller store-brand package often has a significantly lower unit price than a larger name-brand package of the same product type. The comparison only becomes obvious when you're looking at both unit prices side by side.

Package-size changes. A product can move from 750 grams to 680 grams while keeping the same shelf price. The unit price makes that change visible.

Package sizes and promotions change. The shelf price alone therefore cannot tell you which option costs less for an equal quantity.

How to read a unit price on a shelf tag

When a shelf tag includes a unit price, it is often printed below the main price. It may look like this:

$5.49 $1.10 / 100 g

The top number is what you pay at checkout. The bottom number is the cost per 100 grams — that's the one you want to compare.

A few things to watch for:

• Units aren't always consistent. One tag might show per 100g, another might show per kg. Convert them to the same unit before comparing. Per 100g and per 100mL are both common for food; per unit is common for things like paper towels or eggs.
• Check the calculation. If the printed unit price and displayed package price do not appear to match, divide the price by the quantity yourself and confirm the final price before buying.
• Some products do not display a unit price. In that case, divide the package price by the weight, volume, or item count shown on the package.

Where unit pricing matters most

Some product categories show wider unit-price variation than others. These are worth paying attention to:

Cooking oils. Compare bottles and jugs by price per 100 millilitres. Then choose a quantity you can store and use.

Dry staples (rice, pasta, flour, oats). Similar principle. If you eat it regularly and it keeps well, unit price comparison pays off quickly.

Cheese. Blocks, slices, and shredded cheese can have different unit prices. Compare the price per 100 grams, then decide whether the prepared format is worth the difference.

Cleaning and household products. For dish soap, laundry detergent, and similar products, compare equal units and check concentration or directions for use.

Beverages. Bottles, cans, boxes, and jugs can hold very different quantities. A price per 100 millilitres puts those formats on equal terms.

Make unit pricing part of your weekly shop

The good news is that you don't need to calculate anything manually once you get used to looking in the right place.

A simple approach that works for most people:

1. Pick one category to focus on per trip. Trying to optimize every product at once is exhausting. Spend two minutes in the cooking oil aisle this week. Spend two minutes in the pasta aisle next week. Over a month, you've covered your staples without it feeling like a homework assignment.

2. Note the unit price when you find your go-to products. You don't need to comparison-shop every week. Once you know which size of a product you regularly buy has the best unit price, you can just buy that one on repeat — and only check again when you see a sale.

3. Be skeptical of "value pack" framing. The word "value" on a package doesn't guarantee a better unit price. Check the tag.

4. Don't optimize everything. Some products are worth paying a small premium for in a more convenient format — that's a fine choice. The goal isn't to squeeze every cent out of every purchase, it's to make sure the tradeoffs you're making are ones you're actually choosing, not ones you're making by accident.

The bigger picture

Unit pricing is one part of the comparison. It tells you the cost per gram or per millilitre, but not whether a product is on sale, whether another retailer result has a lower price, or how the product fits into the rest of your cart.

The most useful thing unit pricing gives you is a fair comparison point. It lets you compare the price of an equal quantity even when package sizes differ.

That's worth a few seconds of attention.

Search Vynn to compare available package and unit prices across retailers before you head to the store. Coverage varies by product and location. Search grocery prices.