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Shrinkflation Calculator

Shrinkflation is when a product's pack gets smaller while the price holds or drops by less, so you pay more for what you actually get. This calculator puts numbers on it: enter the price and size of the old and the new pack of the same product, and it works out how the unit price has really changed. Everything runs in your browser.

Compare the old and the new pack of the same product by price and quantity. The tool reports the arithmetic only – unit price per kg, l or piece and the changes. It makes no legal judgement and measures no quality. All defaults are example assumptions; the calculation runs in your browser and nothing is stored.

Old package
New package

What your result means

Each card shows a part of the comparison: the old and new unit price side by side, then the package, price and effective changes. The effective change is the one to trust, because a smaller pack at an unchanged price can still add up to paying more. The value-preserving figures put that in everyday terms: the price the new pack would need for nothing to have changed, and the amount your money would have bought at the old rate. A short, neutral line rounds it off: whether the size, the price or both moved, and which way the unit price went.

How this calculator works

Shrinkflation is a business practice, not a figure in its own right: a maker or retailer trims the contents of a pack while holding the price or cutting it by less. The calculator looks at that arithmetically, through the unit price (the price per kg, litre or piece), because that is where a smaller pack shows up as a genuine increase, even when the sticker price hasn't moved.

To compare the two packs fairly, it first converts each size to a common base (grams for mass, millilitres for volume, or a plain count) and then to a reference unit of a kilogram, litre or piece. The unit price is simply the price divided by that quantity. Both packs have to use the same type of measure: weight against weight, count against count. Weighing a mass against a volume is treated as an input error rather than a guess.

Three figures come out of this. The package change sets the new size against the old, the price change sets the two prices against each other, and the effective change tracks the unit price, the one that pulls both together and the one worth watching. Alongside them, the value-preserving new price shows what the new pack would need to cost to hold the old unit price, and the value-preserving new quantity shows how much you would get for the new price at that old rate. The working is done unrounded and rounded only on screen.

Formula and variables

uA = pA / qAuN = pN / qNΔqty = (qN / qA − 1) · 100Δprc = (pN / pA − 1) · 100Δeff = (uN / uA − 1) · 100pV = uA · qNqV = pN / uA
pA
price of the old pack
qA
old-pack quantity in the reference unit (kg, l or piece)
uA
old unit price per reference unit
pN
price of the new pack
qN
new-pack quantity in the reference unit
uN
new unit price per reference unit
Δqty
package change, in per cent
Δprc
sticker-price change, in per cent
Δeff
effective unit-price change, in per cent
pV
value-preserving new price: new quantity at the old unit price
qV
value-preserving new quantity: new price at the old unit price

Worked examples

Example 1: same headline price, smaller pack

Example inputs
Old price€2.49
Old quantity500 g
New price€2.49
New quantity400 g
Example results
Unit price old (per kg)€4.98
Unit price new (per kg)€6.23
Package change−20%
Price change0%
Effective change+25%
Value-preserving new price€1.99
Value-preserving new quantity500 g

The sticker price stays at €2.49, but the pack shrinks from 500 g to 400 g (−20%). The unit price rises from 4.98 to 6.225 per kg, an effective +25%. At the old unit price the 400 g pack would cost only €1.99 (value-preserving price), or €2.49 would still buy 500 g (value-preserving quantity).

Example 2: fewer pieces and a lower price

Example inputs
Old price€3.00
Old quantity10 pieces
New price€2.80
New quantity8 pieces
Example results
Unit price old (per piece)€0.30
Unit price new (per piece)€0.35
Package change−20%
Price change−6.67%
Effective change+16.67%
Value-preserving new price€2.40
Value-preserving new quantity9.33 pieces

The price falls from €3.00 to €2.80 (−6.67%), but the quantity drops more, from 10 to 8 pieces (−20%). The unit price per piece rises from 0.30 to 0.35, an effective +16.67%. At the old unit price the 8-piece pack should cost only €2.40, or €2.80 would still buy 9.33 pieces.

Assumptions

  • The old and new price are in the same currency; the calculator does not convert currencies.
  • The old and new pack use the same type of measure (mass, volume or count).
  • You are comparing the same product; price and quantity refer to the whole pack each.

Limitations of this calculator

  • No legal judgement: the calculator won't tell you whether a pack change is lawful, deceptive or against the rules; that is a question of consumer law, not arithmetic.
  • No statement about quality, recipe or ingredients; only price and quantity are compared.
  • This is not an inflation or purchasing-power calculator. It compares two packs at one moment, not prices over the years; the inflation calculator covers change over time.
  • You can't compare across different types of measure (weight against volume, say), and the calculator rejects it rather than guess.
  • No live prices are fetched and no inputs are stored; every result is approximate and comes without guarantee.

Common misconceptions

  • Reading only the sticker price: An unchanged sticker price can still hide a higher unit price if the pack shrank; the effective change is the figure to watch.
  • Mixing types of measure: Weight (g, kg), volume (ml, l) and count (piece) are different types of measure; the tool compares only like with like and rejects a mixed entry.
  • Comparing two different products: The comparison only means something for the same product in two pack sizes. Put one brand against another and recipe or quality differences leak into the figure.

Frequently asked questions

What is shrinkflation?

Shrinkflation is when the maker of a product shrinks the pack while keeping the price the same or cutting it by less than the contents. You get less for your money, and the unit price per kg, l or piece goes up, even when the sticker price looks unchanged. This calculator makes that change visible.

How does the conversion to kg, l or piece work?

The calculator brings both packs to a common base (grams, millilitres or a plain count) and then to the reference unit: kg, litre or piece. That makes 400 g and 0.5 kg directly comparable. The unit price is the price divided by that quantity.

Can I compare grams with millilitres?

No. Weight, volume and count are different types of measure, so the calculator only compares like with like: weight against weight, volume against volume. Mix them and it flags the entry rather than guessing.

Does the calculator say whether a pack is a rip-off?

No. It sticks to the arithmetic (how quantity, price and unit price have changed) and doesn't judge whether a change is fair, deceptive or against the rules. For the legal side, a consumer-protection body is the neutral place to ask.

Are my inputs stored?

No. The calculation runs entirely in your browser. No inputs are stored, sent on or analysed, and no live prices are fetched.

Sources and further reading

Official and independent sources on this topic. The links open each website in a new tab; no content is loaded from them into this page.

Spotted an error in the calculation or the text?

If you notice something that is wrong or unclear: let us know via the contact page. We review every report.

Last reviewed: 23/09/2026 · All calculations run in your browser – inputs are not stored. ·How we check our calculators