Unit price calculator
Enter the shelf price and size of two to six products, and the unit price calculator shows which one costs less per ounce, per 100 grams, per fluid ounce or per item, and by how much. It counts multipacks and converts between units, so a 64 fl oz bottle can go up against a gallon jug. Nothing you type leaves your browser.
How unit price is worked out
Unit price is the package price divided by how much is in the package:
unit price = price ÷ (size × number of packs)
A 16 oz jar of peanut butter at $3.49 costs $3.49 ÷ 16 = $0.218 per ounce. A 24 oz jar at $4.79 costs $0.200 per ounce. The bigger jar is about 9% cheaper for the same peanut butter, even though its sticker price is $1.30 higher.
When two packs are labeled in different units, one has to be converted before you divide. The calculator uses the exact definitions of the US units, which NIST lists in SP 811:
| Unit | Equals |
|---|---|
| 1 ounce (weight) | 28.35 g |
| 1 pound | 16 oz, or 453.59 g |
| 1 US fluid ounce | 29.57 ml |
| 1 US pint | 16 fl oz, or 473.18 ml |
| 1 US quart | 32 fl oz, or 946.35 ml |
| 1 US gallon | 128 fl oz, or 3.785 l |
An ounce of weight and a fluid ounce are different things. One measures mass, the other volume, and they only line up for liquids about as dense as water. That's why the calculator won't compare a product sold by weight with one sold by volume: the answer would depend on a density that neither label prints.
Multipacks and prices per item
For a multipack, enter the size of one can or bottle and the number of packs. A 12-pack of 12 fl oz cans at $7.99 holds 144 fl oz, so it costs $0.055 per fluid ounce. A 2 liter bottle at $2.49 holds 67.6 fl oz and costs $0.037 per fluid ounce.
For things sold by count, like eggs, paper towel rolls or dishwasher pods, choose "item". Count only works when the items are the same size, though. Paper towel rolls vary a lot between brands, so if the packs list sheets, enter the number of sheets as items and compare per sheet instead.
Why the shelf tag doesn't always settle it
No federal law makes US stores show unit prices. According to NIST's guide to state pricing laws, a group of states that includes Connecticut, Massachusetts, New Jersey, New York and Oregon requires them, some others have voluntary rules, and most have none. Where a store does show unit prices, the model regulation in NIST Handbook 130 says it should express every size of the same product in the same unit.
Tags still disagree in practice. A per-ounce price on one brand and a per-count price on the one beside it is common, and so is a sale sign that shows only the new total. Those are the cases this calculator is for.
The same regulation lets a store show a unit price under a dollar either to the whole cent or to a tenth of a cent. The calculator always shows the tenth, so two products 0.4 cents apart per ounce don't both read $0.22.
When the bigger pack isn't the better buy
Unit price compares what you pay, not what you eat. A 1 lb clamshell of salad greens at $5.99 costs $0.374 an ounce, well under the $0.698 of a 5 oz box at $3.49. If half the big box wilts before you use it, though, the greens you ate cost $0.749 an ounce, more than the small box. The rule behind that is one line long, and we put a table to it in is buying in bulk cheaper: the bigger pack only wins when its discount is larger than the share you throw away.
So for anything perishable, check what you already have and how fast you get through it before buying the big size. A pantry inventory list answers the first question, and noting dates in an expiration date tracker answers the second. For staples that keep, like rice, dried beans or canned tomatoes, take the lower unit price if you have the space.
The unit prices you pay also tell you more over months than on one shopping trip. Logged for the handful of staples you buy every week, they show which prices are creeping up and when a pack quietly got smaller. Our guide to tracking grocery spending covers how to do that from receipts.
Questions
How do I calculate price per ounce?
Divide the price by the number of ounces. $2.99 for a 12 oz box is $2.99 ÷ 12 = $0.249 per ounce. If the size is in pounds, multiply by 16 first. If it's in grams, divide the grams by 28.35 to get ounces.
How do I compare a price per pound with a price per ounce?
Divide the price per pound by 16. $3.20 a pound is $0.20 an ounce. In the calculator, pick either unit in the "Compare" menu and both products are shown in it.
What does the unit price on a shelf tag mean?
It's the price of one standard unit of the product (an ounce, a pound, 100 grams, a fluid ounce or one item), printed beside the total price so packs of different sizes can be compared. Each store picks the unit, and whether it has to show one at all depends on the state.
How much should my groceries cost in the first place?
That depends on who you're feeding. The grocery budget calculator works it out from USDA's monthly food plans for each person's age and sex.