Grocery packaging makes "which one is cheaper" surprisingly hard to answer at a glance — different sizes, different brands, different units on the label. The fix is always the same: find the unit price (the cost per ounce, pound, or liter) for each option and compare those, not the total price on the sticker. Below are worked examples using real grocery items, step by step.
The Formula
Unit price = Total price ÷ Total quantity
Calculate this for both options, using the same unit for both, then compare. Whichever number is lower is the better deal on a per-unit basis — though as the mistakes section below covers, per-unit price isn't the only thing worth considering.
Worked Example Problems
A name-brand cereal costs $3.00 for an 18-ounce box. A store-brand costs $2.80 for a 14-ounce box. Which is the better deal per ounce?
Name brand: $3.00 ÷ 18 = $0.1667 per ounce. Store brand: $2.80 ÷ 14 = $0.20 per ounce. The name brand is actually cheaper per ounce, even though it costs more at the register — the lower total price on the store brand doesn't win here because the package is smaller.
Orange juice comes in a 1-liter bottle for $3.00, or a 2-liter bottle for $5.00. Which is the better deal?
1-liter: $3.00 ÷ 1 = $3.00 per liter. 2-liter: $5.00 ÷ 2 = $2.50 per liter. The 2-liter bottle is the better deal, at $2.50 per liter.
Rice is sold in a 5 lb bag for $6.00 or a 10 lb bag for $11.00. Which costs less per pound?
5 lb bag: $6.00 ÷ 5 = $1.20 per pound. 10 lb bag: $11.00 ÷ 10 = $1.10 per pound. The 10 lb bag is cheaper, at $1.10 per pound.
Peanut butter comes in a 16 oz jar for $3.20 or a 40 oz jar for $7.60. Which is the better value?
16 oz: $3.20 ÷ 16 = $0.20 per ounce. 40 oz: $7.60 ÷ 40 = $0.19 per ounce. The 40 oz jar is cheaper, but only by a penny per ounce — a case where the "bulk discount" is real but small.
Olive oil is $8.00 for a 500 ml bottle or $14.00 for a 1-liter bottle. Which is the better deal per liter?
500 ml = 0.5 liters, so: $8.00 ÷ 0.5 = $16.00 per liter. The 1-liter bottle: $14.00 ÷ 1 = $14.00 per liter. The 1-liter bottle is cheaper, at $14.00 per liter.
Ground coffee is $9.00 for 12 ounces or $22.40 for 32 ounces. Which is the better deal per ounce?
12 oz: $9.00 ÷ 12 = $0.75 per ounce. 32 oz: $22.40 ÷ 32 = $0.70 per ounce. The 32-ounce bag is cheaper, at $0.70 per ounce.
Eggs cost $3.60 for a dozen (12), or $5.22 for an 18-count carton. Which is the better deal per egg?
Dozen: $3.60 ÷ 12 = $0.30 per egg. 18-count: $5.22 ÷ 18 = $0.29 per egg. The 18-count carton is cheaper, by a penny per egg.
Common Mistakes When Comparing Unit Prices
Assuming the bigger package always wins. The cereal example above shows why this fails — a smaller package can have the lower unit price. Always calculate; don't assume.
Comparing different units without converting first. A price listed per ounce can't be compared directly to a price listed per pound, or per liter to per milliliter. Convert both numbers to the same unit before dividing.
Ignoring quantity surcharges. Some brands price larger sizes at the same or even a higher per-unit cost than the smaller size — retailers sometimes count on shoppers assuming "bigger means cheaper" and skipping the math. This is uncommon but real, which is exactly why doing the actual division matters.
Buying more than you'll use before it spoils. A lower unit price only saves money if you actually use what you bought. This applies especially to fresh ingredients — see the bulk buying section on the cost per serving calculator for more on when bulk sizes do and don't pay off.
Frequently Asked Questions
What is unit price?
Unit price is the cost of one standard unit of a product — one ounce, one pound, one liter, or one item — rather than the total price of the whole package. It's the only way to fairly compare two packages that are different sizes, since the total price alone doesn't tell you which one is actually cheaper per amount.
How do I calculate unit price if the shelf tag doesn't show it?
Divide the total price by the total quantity: unit price = total price ÷ total amount. For example, a $4.50 bag that holds 30 ounces costs $4.50 ÷ 30 = $0.15 per ounce. Make sure both packages you're comparing use the same unit — convert pounds to ounces, or liters to milliliters, before dividing.
Is the bigger package always the better deal?
No. Larger packages are usually cheaper per unit, but not always — some brands charge a similar or even higher per-unit price on the large size (sometimes called a quantity surcharge). The only way to know for sure is to actually calculate and compare the unit price, not just assume the bigger box wins.
Do I need to convert units before comparing prices?
Yes, always compare apples to apples. If one package lists ounces and the other lists pounds, convert one to match the other (1 pound = 16 ounces) before dividing by price. Comparing a $/oz price directly to a $/lb price without converting will give you the wrong answer almost every time.