Comparing by unit price
Bigger packages are often, but not always, cheaper per unit. Shelf tags in many US states show a unit price, but they sometimes use different units for similar products (per ounce vs per count), which makes comparing hard. Dividing each price by its size puts both on the same footing.
Worked example
Coffee: Option A is 500 g for $3.49, option B is 1,000 g for $5.99.
- A: 3.49 ÷ 500 = $0.00698 per gram
- B: 5.99 ÷ 1,000 = $0.00599 per gram
Option B is cheaper per gram, by about 14.2%. Buying 1 kg as two 500 g packs would cost $6.98, almost a dollar more.
When the bigger pack is not the better deal
- It spoils before you finish it.
- A sale or coupon on the small size can flip the comparison; run the numbers with the sale price.
- "Family size" packs occasionally cost more per unit than two regular ones.
Make sure both sizes use the same unit: convert pounds to ounces or liters to milliliters first.
How this works
The page divides each price by its size to get the unit price, then compares the two. The savings figure is the difference between the unit prices divided by the higher one, so it says how much less you pay per unit with the cheaper option. Both sizes must use the same unit. Everything runs in your browser.
Frequently asked
How do I calculate unit price?
Divide the price by the size: $5.99 ÷ 1,000 g = $0.006 per gram.
Is the bigger package always cheaper?
No. Check the unit price; sales on smaller sizes and family-size packs can reverse it.
What if the sizes use different units?
Convert them first, for example 1 lb = 16 oz or 1 L = 1,000 mL.
What does the savings percentage mean?
How much less the cheaper option costs per unit, compared with the more expensive one.
Sources
- Lei nº 10.962/2004 — afixação de preços, art. 2º-A: preço por unidade de medida
- Wikipedia — Unit price
Reviewed Oct 17, 2026 · test vectors fixtures/calculators/everyday/unit-price-calculator/