THE SHORT ANSWER
Compare unit prices, not just the price tag
Divide each price by its package size, then calculate the percentage change. A package shrinking from 16 oz to 14 oz at the same price raises the unit price by about 14.29%.
Why a smaller package can hide a price increase
Imagine a product staying at $4.99 while its package changes from 16 oz to 14 oz. These are hypothetical prices and sizes. The sticker price is unchanged, but you receive less for the same amount of money.
Unit price puts both packages on equal footing. It answers the practical question: how much does one ounce, one fluid ounce, or one item cost before and after the change?
Work through the 16 oz to 14 oz example
Scroll sideways to see the full table.
| Package | Price | Size | Price per oz |
|---|---|---|---|
| Before | $4.99 | 16 oz | About $0.3119 |
| After | $4.99 | 14 oz | About $0.3564 |
Divide $4.99 by 16 for the old unit price and by 14 for the new one. The package is 12.5% smaller, but the unit price rises by about 14.29%. Those percentages differ because the price increase is measured from the lower, original unit price.
Shrinkflation formula
Use the original prices and amounts: (($4.99 ÷ 14) ÷ ($4.99 ÷ 16) − 1) × 100 ≈ 14.29%. Keep full precision until the final answer; dividing the rounded unit prices in the table would give a slightly different result. At the new rate, 16 oz would cost about $5.70. That is an equivalent-quantity comparison, not a package you can necessarily buy.
What if the price and package size both change?
The following hypothetical examples start with a $4.00, 16 oz package: $0.25 per oz. Each row is a separate replacement for that original package.
Scroll sideways to see the full table.
| New package | Price per oz | Unit-price change |
|---|---|---|
| $4.40 for 16 oz | $0.2750 | +10% |
| $4.00 for 14 oz | About $0.2857 | About +14.29% |
| $4.40 for 14 oz | About $0.3143 | About +25.71% |
For the last row, ((4.40 ÷ 14) ÷ (4.00 ÷ 16) − 1) × 100 ≈ 25.71%. Adding the 10% sticker-price increase to the 12.5% size decrease would give the wrong answer: the new price is being spread across fewer ounces.
For your own comparison, record the date, regular or sale price, and total package amount for both versions. Compare similar purchase conditions; a temporary sale ending is different from a package redesign. The calculator measures the change without determining its cause.
Can a lower sticker price still mean a higher unit price?
Yes. Starting with the same $4.00, 16 oz package, suppose the replacement costs $3.75 for 14 oz. You pay 25 cents less at checkout, but each ounce now costs about $0.2679 instead of $0.25—an increase of about 7.14%.
At $3.50 for 14 oz, the unit price would stay at $0.25. Both the sticker price and package size would have fallen by 12.5%. Compare the two unit prices before calling the smaller package a better deal.
Make the comparison fair
- Use the same unit. Convert both packages to ounces, fluid ounces, pounds, grams, milliliters, or count before comparing.
- Check multipacks carefully. Compare the total quantity in the entire package, not just the number of inner packs.
- Remember what the math leaves out. Ingredients, quality, packaging, and convenience may also change.
The unit-price result describes the size and price change. It does not determine why the manufacturer changed the product.
The U.S. Bureau of Labor Statistics also explains smaller packages at the same price in terms of unit prices in its overview of shrinkflation. The calculations here compare individual packages; they do not measure the overall inflation rate.