Unit Price Comparison and Shrinkflation: Which Size Is Really Cheaper?
October 29, 2026
Unit price is the price divided by the quantity, such as dollars per ounce, per 100 grams, or per sheet. It lets you compare different package sizes and brands on equal terms. Many stores display it on the shelf tag, but units may differ between products, making direct comparison hard.
A 12-ounce cereal box costs $3.49, so the unit price is $3.49 ÷ 12 = $0.2908 per ounce. An 18-ounce box costs $4.99, or $0.2772 per ounce, 4.7% cheaper per ounce. If you finish the cereal before it goes stale, the larger box saves $0.0136 per ounce, or about $0.24 for the 18 ounces.
Skip the math and get your answer instantly:
Open the Percentage Calculator →Shrinkflation
Shrinkflation is when a manufacturer reduces the package size while keeping the price the same (or nearly). The effective price increase = old size ÷ new size − 1. A 16-ounce bag that becomes 14.5 ounces at the same price: 16 ÷ 14.5 − 1 = 10.3% more per ounce. A 12-pack that becomes a 10-pack at the same price is a 20% increase. Always compare unit prices when you shop and check the quantity on the label: if you buy the same product every week, track the price and size. The percentage looks smaller than the effect on your budget over a year.
| Item | Price | Size | Unit price |
|---|---|---|---|
| Cereal, small | $3.49 | 12 oz | $0.291 / oz |
| Cereal, large | $4.99 | 18 oz | $0.277 / oz |
| Chips, old size | $4.00 | 16 oz | $0.250 / oz |
| Chips, shrunk | $4.00 | 14.5 oz | $0.276 / oz (+10.3%) |
| Detergent | $12.99 | 64 loads | $0.203 / load |
When Bigger Isn't Cheaper
Bulk is not always a better deal: warehouse packs sometimes have a higher unit price than the sale price of a smaller package. Waste from spoilage cancels the saving: if you throw away 25% of a bulk perishable, the effective unit price is 33% higher (1 ÷ 0.75 = 1.33). Include storage cost and the upfront cash. Compare using the same unit, converting as needed: 1 pound = 16 ounces = 453.6 g; 1 liter = 33.8 fluid ounces; 1 gallon = 128 fluid ounces. A 2-liter bottle at $1.99 is $0.0295 per fluid ounce; a 12-pack of 12-ounce cans at $6.99 is $0.0485 per fluid ounce.
Practical Tips
Carry a calculator (your phone), or compare by finding the price per 100 g or per ounce. Compare brand and store-brand products, and use per-use units for items such as detergent (per load), paper towels (per 100 sheets), and diapers (per diaper). Coupons change the unit price: apply them before comparing. Track prices of staple items in a notebook or app to see when a 'sale' is actually a good price.
Take Note
Quality, nutrition, and ingredients also matter, as does what you will actually consume. The lowest unit price is the best value only for equivalent products.
Frequently Asked Questions
How do I calculate unit price?
Divide the price by the quantity.
What is shrinkflation?
Reducing the package size while keeping the price, which raises the effective price.
How do I find the effective price increase from shrinkflation?
Old size divided by new size, minus 1.
Is the bigger package always cheaper?
No, check the unit price and consider waste.
Why convert units?
To compare products listed in different units.