Orpheus

Which Size Is Actually Cheaper?

Price per unit for two packs, side by side.

Inputs
Show price per
Option B is cheaper
0.47 per 100
Option A · 500 for 2.5
0.5 per 100
Option B · 900 for 4.2
0.47 per 100
Difference
6.67%
Cost of A's quantity at B's rate
2.33
unit price = price ÷ quantity

The larger pack (B) is 6.67% cheaper per unit, which is the usual direction.

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Divide each price by its quantity to get a price per unit, then compare. A 500 g pack at 2.50 is 0.50 per 100 g; a 900 g pack at 4.20 is 0.47 — the larger one is about 7% cheaper.

How to use Unit Price Comparison

  1. Enter both prices and sizes. Use the same unit for both — grams against grams, sheets against sheets.
  2. Pick a comparison basis. Per 100 units is the usual supermarket convention.
  3. Read which wins. And by what percentage.

About comparing unit prices

Unit pricing is the only reliable way to compare pack sizes, and the reason it needs a tool at all is that the arithmetic is easy while the conditions for doing it are not. Prices and quantities are chosen to be awkward — 425 g at 1.89 against 700 g at 2.99 — and the comparison has to happen at a shelf, in a few seconds, against a label that may express the two in different bases. The general expectation that larger packs are cheaper per unit holds most of the time and fails often enough that checking is worthwhile. Promotions are the usual reason: a multi-buy or a temporary discount is frequently applied to the smaller size, which inverts the relationship for as long as it runs. Premium formats, single-serve packaging and anything sold on convenience break it structurally rather than temporarily. Shelf-label unit pricing is mandated in many jurisdictions and remains inconsistent in practice, with adjacent products priced per 100 grams and per kilogram, or per item and per sheet, in ways that cannot be compared at a glance. The measure is also the most direct way to notice package downsizing, since a reduced quantity at an unchanged price shows up immediately as a higher unit price while the shelf price looks the same. What unit price cannot tell you is whether the purchase is a good idea. A cheaper unit price on a quantity you will not finish is not a saving, and larger packs that increase consumption are a well-documented effect rather than a hypothetical one.

Frequently asked questions

Is the bigger pack always cheaper per unit?
No, and the exceptions are common enough to be worth checking. Promotions frequently discount the small size, and premium or convenience formats break the pattern entirely. Studies of supermarket shelves routinely find a meaningful minority of larger packs costing more per unit.
Why is the shelf label not enough?
Unit pricing on shelf labels is required in many places and is often inconsistent in practice — one product priced per 100 g and the one beside it per kilogram, or per item against per sheet. Different bases cannot be compared by eye, which is exactly where the mistake happens.
What is shrinkflation?
Reducing the contents while keeping the price and packaging similar. It shows up as a rising unit price when the shelf price has not moved, which is why comparing per unit rather than per pack is the only way to notice it.
Does the cheapest unit price always mean buying it?
Not if you will not use it. A larger pack that spoils, goes stale, or occupies storage you do not have is not value, and neither is one that increases how much you consume. The unit price answers a narrow question well and it is not the whole decision.
Can I compare different units?
Only after converting them to a common one. Comparing a price per litre against a price per pint is meaningless as it stands, and it is a mistake that is easy to make when products from different markets sit on the same shelf.

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