Shrinkflation calculator
Enter the pack size and price before and after. You get the real change in price per unit, which is the number the smaller pack is hiding.
Nothing you type leaves your browser. The link in the address bar updates as you type, so you can share a result. Every documented case has a “check the math” link that fills this in.
How it works
How do you calculate shrinkflation?
Divide the price by the size before and after the change to get the price per unit (per gram, ounce, sheet…). The percentage difference between the two unit prices is the real price change. A 10% smaller pack at the same price is an 11.1% price rise per unit, because 1 ÷ 0.9 = 1.111.
Why is the hidden price rise bigger than the size cut?
Because the same price is now spread over less product. Cutting a pack by a fraction x raises the unit price by x ÷ (1 − x): a 20% cut is a 25% rise, a 50% cut is a 100% rise.
What is a fair price for the smaller pack?
Old price × new size ÷ old size. That is what the new pack would cost at the old price per unit.
See the worst offenders for the biggest real price hikes we have on record.