The 20-second shelf check
- Find the quantity: weight, volume, count or usable amount.
- Find the unit price on the shelf label or calculate price divided by quantity.
- Compare products using the same unit.
- Check whether a sale, loyalty price or multipack condition changes the calculation.
What unit price means
Unit price is the cost for a standard amount, such as per kilogram, litre, 100 grams, ounce or item. NIST says consistent unit pricing helps shoppers compare value across different product sizes and brands. Australia’s ACCC similarly describes it as the price using a standard unit of measurement.
Fast rule
Ignore the visual size of the package for a moment. Compare the number beside “per kg,” “per litre,” “per 100 g,” “per ounce” or “each.” The lower comparable unit price is cheaper for the same amount.
Worked examples
| Option | Calculation | Unit price | Better value? |
|---|---|---|---|
| 900 g cereal for $6.30 | $6.30 ÷ 900 × 100 | $0.70 per 100 g | Yes |
| 750 g cereal for $5.70 | $5.70 ÷ 750 × 100 | $0.76 per 100 g | No |
| 6 rolls for $4.20 | $4.20 ÷ 6 | $0.70 each | Compare sheet count too |
How shrinkflation hides in plain sight
Shrinkflation is when a package contains less while its price stays roughly the same. Canada’s Competition Bureau gives the example of a pack changing from 450 grams to 430 grams, a difference that may be hard to notice at a glance. The FTC recommends checking the unit price because packaging can shrink without looking dramatically different.
Five traps unit price may not fully explain
- Different quality: ingredients, concentration or durability can justify a higher unit price.
- Usable quantity: compare drained weight, sheet count, doses or concentrated servings when relevant.
- Loyalty prices: confirm whether the displayed unit price assumes membership or buying several items.
- Waste: a cheaper bulk pack is not cheaper if food expires before you use it.
- Mixed units: convert both products to the same unit before deciding.
When the shelf does not show a unit price
Use a phone calculator: divide the selling price by the quantity. To compare per 100 grams or millilitres, multiply the result by 100. For multipacks, divide by the total number of comparable items, then check whether each item became smaller.
A practical shopping routine
- Photograph or note the weight and price of products you buy repeatedly.
- Compare the unit price across brands and nearby sizes.
- Check the quantity again when packaging changes.
- Choose the lowest sensible unit cost that fits your storage and realistic usage.
- Keep the receipt if the shelf price or advertised offer appears misleading.