The price on the shelf is not the price that matters
A 750 g box at $4.50 and a 1.2 kg box at $6.80 are not directly comparable from their sticker prices alone — one is bigger, one costs more, and the sticker tells you neither which is actually cheaper. Unit price answers the only question that matters for value: cost per gram, per litre, per sheet, per whatever the product is measured in.
Unit price = total price ÷ quantityEnter a price and the quantity or weight it buys, in any unit, and the calculator returns the price per single unit so two differently sized packages can be compared directly.
Worked example
| Package | Price | Size | Unit price |
|---|---|---|---|
| Box A | $4.50 | 750 g | $0.0060 / g — $6.00 / kg |
| Box B | $6.80 | 1.2 kg (1200 g) | $0.0057 / g — $5.67 / kg |
Box B is cheaper per gram despite costing more per box — a difference invisible from the shelf price alone, and the entire reason unit pricing exists.
Where this actually saves money
- Bulk versus regular sizes. A larger pack is usually, but not always, cheaper per unit — store brands frequently break this pattern deliberately.
- Store brand versus name brand in the same aisle, where the packaging sizes rarely match.
- Multi-packs. A "3 for $10" deal is not automatically better than a single unit at $3.20 — do the division.
- Different measurement units on the same shelf. One product priced per 100 g and another per pound cannot be compared by eye at all; convert both to the same unit first.
- Concentrated products such as laundry detergent, where a smaller bottle can cost less per wash despite a higher price per litre.
Why store-shown unit prices are not always trustworthy
Many stores print a unit price on the shelf label, and it is a useful shortcut when it is there — but it is not guaranteed to be correct or consistently measured. Two near-identical products can show unit prices per different bases (per 100 g on one, per kg on the other) making them look easier to compare than they are, and shelf labels are occasionally simply wrong after a price change that the label has not caught up with. When a decision genuinely depends on it — buying in bulk regularly, comparing expensive items — recomputing from the receipt price and package size removes any doubt.