Home›Everyday money

Unit price calculator

Find out which package is cheaper by comparing price per ounce, pound or item, even with “buy 3, pay for 2” deals, and see whether a product shrank and how much that really raised the price.

Educational simulation. Not investment advice. Results are estimates based on the data you enter and do not replace advice from a qualified professional.

Reviewed on Nov 1, 2026

Example: coffee in four package sizes, one on a “buy 3, pay for 2” deal. Leave price or quantity blank to skip a product.

Product A
Product B
Product C
Product D

Your inputs stay only on this browser and are not sent anywhere. Untick to delete them.

——
—

Unit price

What the same amount costs in each option, deals included. The green bar is the cheapest.

Tap the chart to see the values.

Comparison

Next step

Take this page’s results to another calculator with the fields already filled in.

Work out the percentage difference →

The summary lists your inputs, results, formulas, assumptions and sources. The full report also includes the charts and interpretations, in color. In the print dialog, choose Save as PDF.

Method, assumptions and sources

Formulas

Effective price = price × share paid (buy 3 pay 2 = 2/3; buy 2 pay 1 = 1/2; buy 4 pay 3 = 3/4; second item half off = 3/4)
Unit price = effective price ÷ quantity converted (oz, fl oz or count)
Real increase = (price after ÷ size after) ÷ (price before ÷ size before) − 1

Assumptions and limits

  • Conversions: 1 lb = 16 oz = 453.6 g; 1 gal = 128 fl oz = 3.785 L. Only products in the same unit family as the first one entered are compared.

Official sources and references

Frequently asked questions

How do I calculate unit price?

Divide the price by the quantity: a 12 oz bag at $8.99 costs $8.99 ÷ 12 = $0.749 per ounce, or $11.99 per pound. The calculator converts ounces, pounds, fluid ounces, gallons and metric units automatically.

How do I read the example result?

Of the four coffee packages, D (12 oz at $9.49 on a buy-3-pay-for-2 deal) works out to $0.527 per ounce, 15.6% less than the next best, C ($0.625). The most expensive is A, the 12 oz bag at full price, which costs 42.1% more per ounce than D.

Is the bigger package always cheaper?

No. It often is, but deals, brands and in-between sizes change the math. That is why the unit price is the number to compare, not the package size or the shelf price.

Is “buy 3, pay for 2” always a good deal?

Only if you will use everything before it expires and the unit price beats the other options. The deal cuts the effective price to 2/3 but makes you buy more; with perishables, waste wipes out the discount.

What is shrinkflation?

It is when a maker shrinks the package and keeps the price the same or raises it slightly. In the “Did the product shrink?” example, a cereal box goes from 18 oz to 15.4 oz at the same $4.99: the price per ounce rises 16.9%.

Do stores have to show unit prices?

It depends on the state. Some states require unit pricing on shelf tags, and NIST publishes a uniform guideline that many retailers follow voluntarily. When a tag shows it, check that you are comparing the same unit.

What are the limits of this calculator?

It only compares products measured the same way (weight with weight, volume with volume, count with count) and does not judge quality, brand or yield. For concentrated products like detergent, compare by number of loads when the label shows it.

Related calculators

See all in Everyday money ›

Unit price calculator: which package is really cheaper

Packages of different sizes can only be compared by unit price: what one ounce, one pound or one item costs. The math is simple: price ÷ quantity. With a “buy 3, pay for 2” deal, use the effective price: price × 2/3.

Example

A 12 oz bag of coffee at $8.99 works out to $0.749 per ounce; 24 oz at $15.49 to $0.645; a 2 lb bag at $19.99 to $0.625. A 12 oz bag at $9.49 on a buy-3-pay-for-2 deal comes to $0.527 per ounce, the cheapest, as long as you buy all three.

ProductPricePer ozPer lb
A · 12 oz$8.99$0.749$11.99
B · 24 oz$15.49$0.645$10.33
C · 2 lb$19.99$0.625$10.00
D · 12 oz, buy 3 pay 2$9.49$0.527$8.44

Shrinkflation

When a package shrinks and the price stays the same, the increase never shows on the shelf tag. A cereal box that goes from 18 oz to 15.4 oz at the same $4.99 is 16.9% more expensive per ounce.

Reading shelf tags

Many stores show the unit price in small print on the shelf tag, following NIST’s unit pricing guidelines. Make sure two tags use the same unit (per ounce vs. per pound, per count vs. per ounce) before comparing.