Unit price calculator
Enter each package's price and size, see which is the better buy.
How do I calculate the unit price?
Divide the price by the amount: a 16 oz jar for $3.99 costs $3.99 ÷ 16 = $0.249 per ounce. The lower unit price is the better deal.
Is the bigger package always cheaper?
Often, not always. A 2 lb bag for $6.49 is $0.203 per ounce (32 oz) — cheaper than the 16 oz jar above — but sales and store brands regularly beat the big size.
How do I compare packages in different units?
Convert them to the same unit first — the calculator does it: pounds and grams to ounces, liters to fluid ounces. Weight and volume cannot be compared directly, since a fluid ounce of honey weighs more than one of water.
What about "per count" items?
Pick "per item" to compare packs of eggs, diapers or batteries: 18 eggs for $4.29 is 23.8¢ each against 12 for $2.99 at 24.9¢.
Doesn't the store shelf tag show this?
Many do, but not all states require unit pricing, and tags sometimes use different units for similar products (per ounce vs per pound). Entering the price and size yourself avoids that.
How do I compare a multipack with a single large bottle?
Multiply the count by the size of each unit to get the total, and enter that. Twelve 12 fl oz cans for $6.99 are 144 fl oz in total, or 4.85¢ per fl oz. A 2 liter bottle for $1.99 is about 67.6 fl oz, or 2.94¢ per fl oz, so here the bottle is cheaper per ounce, even though it feels like a smaller purchase.
What is shrinkflation and how does unit price show it?
Shrinkflation is when a package gets smaller at the same price. A 12 oz box at $4.49 costs 37.42¢ per ounce; if the box is cut to 10.5 oz at the same price, it is 42.76¢ per ounce, an increase of 14.3% with no change on the price tag. Comparing unit prices over time is the way to see it.
How the comparison works
Each package's price is divided by its size after the size is converted to a common unit: ounces, pounds, grams, kilograms, fluid ounces, quarts, gallons, milliliters, liters or a plain count. The results are shown per ounce, pound, 100 g, kilogram, fluid ounce, liter or item, whichever you pick, and the cheapest is highlighted with the percentage it saves over the most expensive. Weight and volume cannot be converted into each other without knowing the density of the product, so a package measured by weight is never compared with one measured by volume; it is left out and the page says so.
Worked example: three boxes of cereal
A 12 oz box costs $4.49, a 20 oz box $6.79 and a 2.5 lb club-size bag $11.99. Convert to ounces: the bag is 2.5 × 16 = 40 oz. The unit prices are 37.42¢, 33.95¢ and 29.98¢ per ounce, so the best buy is the club bag. The difference between the best and the worst is 19.9%. The cheapest per ounce is not always the right purchase if the larger box goes stale before you finish it.
When the lowest unit price is not the best deal
A lower price per ounce saves money only on what you use. Fresh food that spoils before it is eaten, a freezer or pantry with no space, and a large size of something you may dislike all make the cheaper unit price a poorer deal. Coupons, loyalty prices and store brands change the real price, so enter the price you will actually pay at the register. Compare like with like: different grades, concentrations (such as laundry detergent loads, not ounces) or number of sheets (toilet paper in sheets or square feet, not rolls) need the right unit.
Common mistakes
Forgetting to multiply by the count of a multipack is the most common one: the size field wants the total, not the size of one unit. The second is mixing weight and volume. The third is using the drained weight, net weight or the serving size inconsistently, because labels may differ between products. A "per item" comparison is only meaningful when the items are the same size. And a price tag may show the unit price for a different unit than you chose (per ounce or per pound), so convert before comparing shelf labels.
Sources: unit conversions from NIST Handbook 44, Appendix C (ounce, pound, fluid ounce, quart, gallon, liter) and NIST SP 811; unit pricing is the price divided by the quantity in a common unit. Related: discount calculator, percentage calculator and price per square foot calculator.