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4.2

Comparing unit prices

Divide the price by the amount, in the same unit, before you assume bigger is cheaper.

Soda cans on supermarket shelves, with price tags.
Photo: 乾 黄 / Pexels
Area: MoneyFrom age 12Time to learn: 15 minutes

You will be able to tell which package size is the better deal per ounce or per gram.

Why it matters

Bigger packages are often cheaper per unit, but not always, and sales can flip the answer. In the US there is no federal rule requiring shelf unit prices; a 2015 federal guide listed only nine states and DC that required them. Grocery prices keep rising, so the habit pays every week.

US food-at-home (grocery) prices were 2.2% higher in August 2026 than in August 2025.
Source: USDA Economic Research Service, Food Price Outlook, 2026.Measured

How to do it

  1. Look for the unit price on the shelf tag, usually in small print, such as '$0.19 per oz' or '$0.90 per 100 g'.
  2. Check that both tags use the same unit. One may say per ounce and the other per pound or per count.
  3. If there is no unit price, divide the price by the amount: $4.56 for 24 oz is $4.56 ÷ 24 = $0.19 per ounce.
  4. Do the same for the other size: $3.20 for 16 oz is $0.20 per ounce. Here the 24 oz package is cheaper per ounce.
  5. Convert units if needed: 1 pound = 16 ounces; 1 kg = 1,000 g. For metric, price per 100 g = price ÷ grams × 100.
  6. Try a metric check: 500 g for $4.00 is $0.80 per 100 g; 750 g for $6.75 is $0.90 per 100 g. Here the smaller pack wins.
  7. Recheck during sales and multi-buy deals, like '3 for $5', which can change the answer.
  8. Buy the bigger size only if you will use it before it spoils or expires.

Common mistakes

  • Assuming the bigger package is always cheaper.
  • Comparing a per-ounce tag with a per-pound tag.
  • Buying in bulk and throwing half of it away.
You can do this when …you can work out the price per ounce or per 100 g for two sizes in under a minute, in your head or with a phone calculator.

Sources

  1. NIST Special Publication 1181: Unit Pricing Guide
  2. USDA Economic Research Service: Food Price Outlook summary findings

Sources and numbers last checked . How we check

Go deeper

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