Price per kilogram: the only comparable figure on a price tag

There are two numbers on a price tag. The large one is what you pay at the register, and you cannot compare anything by it: products have different volumes. The small one is the price per kilogram or liter, and it is the only number on the shelf that is comparable between packages. It also counters almost all the tricks used to confuse shoppers.

What this figure is

The unit price—per kilogram, liter, hundred grams, or per item—is provided on the price tag next to the main price, usually in a noticeably smaller font. It is calculated from the price and the actual volume of the package, and therefore does not depend on the size of the pack, promotions, or how the product looks.

You can compare everything by it: two brands of the same product, a large package with a small one, or a product on sale with one that is not.

What it shows immediately

Shrinkflation. The pack has gotten smaller, but the price is the same—it has become more expensive per kilogram, and this is immediately visible. This tactic is analyzed in our article on shrinkflation.

The false value of large packaging. An "economy" pack is not always cheaper per kilogram: sometimes it is the opposite, because the shopper assumes it is cheaper and does not check.

The real size of a discount. A yellow price tag with a "30% discount" on a product that is simply 40% more expensive than its competitor is a common situation, and the price per kilogram reveals it.

The difference between similar products. 5% cottage cheese and a 5% cottage cheese product sitting next to each other on the shelf differ in both composition and price per kilogram, and not always in the expected direction.

Where it is misleading

Three cases in which comparing by price per kilogram is incorrect.

Different water content. You cannot compare frozen shrimp with and without glaze by price per kilogram: in the second case, you are paying for the product, while in the first, you are partially paying for ice. The same applies to brine in canned goods and injection solutions in meat.

Different concentration. Concentrated juice, dry bouillon, laundry detergent with different dosages. You should compare by the finished product, not by the weight in the package.

Different state of the product. Dry grains and cooked porridge, dry pasta and boiled pasta. Grains absorb water when cooked—this same difference also breaks calorie counting, which is discussed in our article on protein per day.

Hence the rule: the price per kilogram is comparable within the same state of a product. Between different states, it is not.

What else to look at nearby

• Actual net weight. It is on the packaging, not the price tag, and it is what is used in the calculation.
• Product category. "Butter" and "spread," "condensed milk" and "milk-containing product" sit next to each other and differ significantly—see our articles on butter and spreads and condensed milk.
• Ingredients. Cheaper per kilogram often means a different composition, not a better deal. What to look at first is covered in our article on checking ingredients in ten seconds.

How to make this a habit

1. One glance at the bottom of the tag. The number is always in the same place, and after a week, your eye will find it automatically.
2. Compare shelf neighbors, not the price in your memory: memory stores the price per pack, and packs change.
3. Check promotional items carefully. A yellow price tag is the only place where the price per kilogram is sometimes not recalculated; see our article on promotions and price tags.
4. Do not apply the conclusion to the whole category. A good-value brand in one package format may be a bad deal in another.

Count it from a photo

Frequently asked questions

Where is the price per kilogram on the price tag?

Next to the main price, usually in smaller print: per kilogram, liter, one hundred grams, or per unit. It is calculated based on the price and the actual volume of the package, making it comparable across different packs.

Is a larger package always more economical?

No. The "economy" size is sometimes more expensive per kilogram precisely because the buyer assumes otherwise and does not check. Only the unit price provides the answer.

When should you not compare by price per kilogram?

When the water content differs—such as glaze on shrimp or brine in canned goods—the concentration or state of the product varies. It is incorrect to compare dry grains and cooked porridge by weight: during cooking, grains absorb three times their weight in water.

Does this help to see a reduction in package size?

Yes, immediately. If the volume has decreased while the price remains the same, the price per kilogram increases, and this is visible on the price tag even when the packaging looks the same.

How much can one trust a yellow price tag?

The discount is calculated from the price set by the store, so "minus 30%" does not necessarily mean a better deal compared to a neighboring brand. You should compare the price per kilogram of the promotional item with the price per kilogram of a non-promotional one.

Read next

• Shrinkflation: the package got smaller, but the price stayed the same — A liter of milk has turned into 900 milliliters, a dozen eggs into nine, and a chocolate bar has shrunk from 100 grams to 85.
• Promotions and yellow price tags: how they work and when they are worth it — A yellow price tag works not because the price is low, but because it is high-contrast: the eye finds it before it reads the number.
• What to look for in an ingredient list in ten seconds — Reading an entire ingredient list at the shelf is impossible: the print is small, and there is no time.

This article is for general information. It is not medical advice, a diagnosis, or a prescription for treatment or a diet, and it does not replace a consultation with your doctor. If you have a health condition, are pregnant, take medication, or follow a diet prescribed to you, decisions about food belong with your doctor.

Figures from regulations, guidelines and studies are given as they stood when this article was prepared and may since have changed; check them against the primary sources. This article is not advertising, an offer, or individual advice, and neither the author nor the site owner is responsible for decisions taken on the basis of it.