How to use the shrinkflation calculator
- Optionally type the size unit, such as oz or sheets. It is only a label, so use the same unit for both sizes.
- Enter the old price and size, then the new price and size of the same product.
- Add how many packages you buy in a year to see the extra cost of getting the same amount as before.
- Read the unit price change, which compares price per ounce, per sheet or per whatever unit you chose.
Formula
Unit price = package price / package size
Unit price change = new unit price / old unit price - 1
Cost of the old amount at the new unit price = new unit price x old size
Extra per year = (that cost - old price) x packages per year
A price that stays the same while the size drops still raises the unit price.
$4.00 for 16 oz becomes $4.00 for 14 oz
The old unit price is $4.00 / 16 = $0.2500 per ounce and the new one is $4.00 / 14 = $0.2857. The package price did not change, the size fell 12.5%, and the price per ounce rose 14.29%.
To get 16 ounces again you would pay 16 x $0.2857 = $4.57, which is $0.57 more than before. If you buy 52 packages a year the extra cost is about $29.71. Another case: $5.00 for 20 oz that becomes $5.00 for 18 oz raises the price per ounce by 11.11%.
Why unit price is the right comparison
When both price and size change, the package price alone hides what happened. Price per unit puts the old and new versions on the same footing, so a smaller package at the same price shows up as an increase.
The same method works for a larger price with a larger size, or a lower price with a much smaller size. Anything that moves the unit price shows up in the percent change.
What this does not tell you
The tool compares only the numbers you enter. It does not know why a product changed, whether the recipe or quality changed, or whether the old price was on sale. Check that both sizes use the same unit before you compare.
For two different products or brands, use the unit price calculator. To see how much general prices have moved over time try the inflation calculator, and for any plain percent change use the percent change calculator.
Assumptions and limits
- The old and new sizes use the same unit.
- Prices are for one package and are what you pay on a normal day, not a sale.
- The extra yearly cost assumes you want the same total amount as before.
- Quality, ingredients and the reasons for the change are not considered.
Frequently asked questions
What is shrinkflation?
It is a reduction in the size or quantity of a product while its price stays the same or rises. The price per unit goes up even if the package price looks unchanged.
How do you calculate shrinkflation?
Divide each price by its size to get a unit price, then divide the new unit price by the old one and subtract 1. The result is the percent change in the price per unit.
Can I use it when the package price also changes?
Yes. Enter both the new price and the new size. The unit price change combines the two, so it shows the true change in what you pay per unit.
Why does the percent change in size not match the unit price change?
Price per unit uses size in the denominator, so a 12.5% smaller package at the same price raises the unit price by more than 12.5%, in this case about 14.29%.