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The biggest number on a shelf tag is the price of the package. The small number in the corner is the one that tells you if it is a good deal. That small number is the unit price, and learning to use it is the fastest way to stop overpaying for groceries.
The short answer: the unit price is the cost per standard amount, such as per 100 g, per kg, per 100 mL, per litre or per item. To compare two products, compare their unit prices in the same unit. If a tag does not show one, divide the price by the size.
Why the package price misleads you
Package sizes are all over the place. Here are real examples from Ontario flyers between April and September 2026:
- A cereal promotion at $4.00 covered boxes from 210 g to 525 g. The small box works out to $1.90 per 100 g. The big box is 76 cents per 100 g.
- Barilla pasta at $1.77 came in 340 g and 410 g boxes. The smaller box is about 17% more per kilogram.
- A 200 g block of cheese at $4.49 cost $2.25 per 100 g, while a 400 g block at $4.92 cost $1.23 per 100 g.
In every case, the lower sticker price was not the better deal.
How to read a shelf tag
Most grocery shelf tags in Canada show:
- The product name and size, such as "Pasta 900 g".
- The price in large type.
- The unit price in smaller type, such as "$0.22 / 100 g".
- Sometimes a regular price or a sale end date.
The unit price is often in a corner or under the barcode. Many stores print it, but not all, and the layout differs by store.
Where unit prices trip people up
Different units on neighbouring tags
One product may show a price per 100 g and the one next to it a price per kg. Or one shows per 100 mL and another per litre. You cannot compare $0.45 / 100 g with $4.10 / kg until you convert:
- Per kg to per 100 g: divide by 10. $4.10 / kg is $0.41 / 100 g.
- Per litre to per 100 mL: divide by 10.
- Per kg to per lb: divide by 2.2. $2.18 / kg is about $0.99 / lb.
Per item vs per weight
Some products, like diapers, garbage bags or paper towels, may be priced per unit, per sheet or per count. Two packs with different sheet sizes are not directly comparable per sheet. Compare within the same type where you can.
Sale price vs regular unit price
When a product goes on sale, the shelf tag may still show the unit price for the regular price, or the sale tag may cover it. If in doubt, work it out yourself.
Multi-buy offers
"2 for $7" means $3.50 each. Some stores give the sale price even if you buy one; others require you to buy two. Check your store's policy and the flyer's fine print.
Liquid vs dry weight
Canned vegetables and fruit list a total volume (for example, 398 mL), but part of that is liquid. For canned goods, it is fairest to compare products of the same type and size.
How to do it yourself in 10 seconds
You do not need a calculator app, just one rule:
Price ÷ size × standard amount = unit price.
- For price per 100 g: $2.00 ÷ 900 g × 100 = $0.22 per 100 g.
- For price per kg: $2.00 ÷ 900 g × 1,000 = $2.22 per kg.
- For price per litre: $5.49 ÷ 4 L = $1.37 per litre.
A shortcut for comparing two items fast: if one package is twice the size, it needs to be less than twice the price to be a better deal.
Unit price is not the only thing that matters
A lower unit price is only a saving if you use what you buy. Ask:
- Will we finish it before it spoils? A 10 lb bag of potatoes is cheap per pound, but not if half of it sprouts.
- Do we have room to store it? Bulk buys need pantry or freezer space.
- Is it the same product? Store brand, name brand, organic and premium are not always interchangeable. Compare like with like.
Unit price plus price history
Unit price tells you which package is the best value today. Price history tells you if today is a good day to buy at all. A 700 g cheese bar may have the best unit price on the shelf, but if it has recently been $2.79 cheaper on a deep sale, it may be worth waiting.
That is what FlyerHawk does for you: it tracks flyer prices at stores near you, compares each one with that product's normal price, and alerts you when it is a real deal. Try FlyerHawk free for 14 days and let it do the comparing.
Quick reference
| To convert | Do this |
|---|---|
| Per kg to per 100 g | Divide by 10 |
| Per 100 g to per kg | Multiply by 10 |
| Per kg to per lb | Divide by 2.2 |
| Per lb to per kg | Multiply by 2.2 |
| Per litre to per 100 mL | Divide by 10 |
FAQ
What is unit pricing?
Unit pricing is the price of a product per standard amount, such as per 100 g, per kg, per litre or per item. It lets you compare products of different sizes fairly.
Do all Canadian grocery stores show unit prices?
Many stores show a unit price on the shelf tag, but not all, and the units are not always the same from one tag to the next. If you cannot find it, divide the price by the size yourself.
Is the bigger package always cheaper per unit?
Usually, but not always. Sales on smaller sizes can make them cheaper per unit, so always check.
How do I compare a price per kg with a price per 100 g?
Divide the price per kg by 10 to get the price per 100 g, then compare.
