Is the bigger pack always cheaper per unit?

No. Promotions on smaller packs frequently make them cheaper per unit, and multibuy offers are often worse value than the single price once you compare properly.

Should I compare by weight or by volume?

Use whichever the product is sold by, and keep both options in the same unit. For tinned food compare drained weight where it is stated.

What about products sold by count?

Price per item only works when the items are the same size. Two packs of different-sized items need to be compared by weight or volume instead.

Unit Price Calculator

Quick answer

Unit price equals price ÷ quantity. Compare two options by putting both into the same unit — per 100 g, per litre or per item — and the cheaper one is then obvious.

Price per unit

Put both options in the same unit — grams, millilitres or items.

Option A — price

Option A — quantity

Option B — price

Option B — quantity

Option A per 100 units

0.465

Option B per 100 units

0.416

B cheaper by

10.6 %

A negative percentage means option A is the cheaper one per unit.

Supermarkets are required in many countries to display unit prices precisely because pack sizes are designed to defeat comparison. A 750 ml bottle next to a 1.2 litre one, priced a few cents apart, is not a comparison anyone does reliably in their head.

The bigger pack is not automatically cheaper per unit. Promotional pricing on small packs regularly inverts the expected order, and multibuys are frequently worse per unit than the plain single price.

Where the bigger pack loses

Two situations make the larger size worse value even when the unit price is lower. The first is waste: buying three kilograms of something that spoils in a week costs more per unit actually consumed than a smaller pack finished completely.

The second is promotion. A small pack on offer routinely undercuts the family size, which is why comparing the shelf unit price rather than assuming is worth the two seconds it takes.

Making units comparable

Convert both options to the same unit before dividing. Grams and millilitres are easiest because the arithmetic stays whole: 100 g and 100 ml are the conventional comparison bases in European shelf labelling.

Watch for drained weight on tinned goods and for products sold by count where the items differ in size. A price per item is only meaningful when the items are genuinely equivalent.

Frequently asked questions

Is the bigger pack always cheaper per unit?: No. Promotions on smaller packs frequently make them cheaper per unit, and multibuy offers are often worse value than the single price once you compare properly.
Should I compare by weight or by volume?: Use whichever the product is sold by, and keep both options in the same unit. For tinned food compare drained weight where it is stated.
What about products sold by count?: Price per item only works when the items are the same size. Two packs of different-sized items need to be compared by weight or volume instead.

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Updated 2026-09-20 · all calculators. Results are estimates for guidance, not professional advice.