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Formula
Unit price = Price ÷ Quantity
- Price
- what you pay for the package
- Quantity
- the package size, converted to a common unit (oz, lb, g, kg, fl oz, L, mL or count)
What a unit price tells you
The unit price is what a product costs per standard unit of measure, such as per ounce, per pound, per liter or per item. Packages come in so many sizes that the sticker price alone can’t tell you which is the better buy. A $3.99 bottle might be a worse deal than a $6.49 one if the bigger bottle holds twice as much. Putting every option on the same unit makes the comparison fair.
Many US stores print a unit price on the shelf tag, but tags don’t always use the same unit for every size, and online listings often leave it out. The unit price calculator fills that gap.
How to use the unit price calculator
- For item 1, enter the price, the size and its unit. The unit you choose here is the one every item is compared in.
- Enter item 2 the same way. Its unit can differ, for example pounds against ounces, as long as both are weights.
- Add items 3 and 4 if you’re comparing more sizes. Leave them blank otherwise.
- Read the result: the cheapest item and its unit price, how much cheaper it is than the most expensive option, and a table ranking every item.
If you mix a weight with a volume, such as ounces with fluid ounces, the calculator asks you to pick matching units, because there’s no fixed conversion between them.
How to calculate unit price by hand
The formula is Unit price = Price ÷ Quantity, with every quantity in the same unit.
Take two boxes of cereal: 18 oz for $4.49 and 1.5 lb for $5.29.
- Convert 1.5 lb to ounces: 1.5 × 16 = 24 oz.
- Box 1: $4.49 ÷ 18 oz = $0.249 per ounce.
- Box 2: $5.29 ÷ 24 oz = $0.220 per ounce.
- Saving: ($0.249 − $0.220) ÷ $0.249 × 100 ≈ 11.6%.
The larger box costs about 11.6% less per ounce. Over a year of breakfasts, that adds up.
A liquid example
A 64 fl oz bottle of juice costs $3.99 and a 1 gallon (128 fl oz) jug costs $6.49. $3.99 ÷ 64 = $0.062 per fl oz, and $6.49 ÷ 128 = $0.051 per fl oz. The gallon is about 18.7% cheaper per fluid ounce.
Unit conversions for shopping
| From | Equals | Handy for |
|---|---|---|
| 1 lb | 16 oz | Meat, coffee, cereal |
| 1 kg | 35.274 oz, or 2.2046 lb | Imported goods, bulk bags |
| 100 g | 3.527 oz | Snacks, spices |
| 1 gal | 128 fl oz, or 4 qt | Milk, juice |
| 1 qt | 32 fl oz | Broth, yogurt |
| 1 L | 33.814 fl oz | Soda, water, oil |
| 1 dozen | 12 items | Eggs, rolls |
Price per gram and per mL
Imported and metric-labeled products list grams or milliliters. Choose g or mL for item 1 and the calculator compares everything per gram or per milliliter. Those prices are tiny, so many shoppers think per 100 g instead: a 250 g pack for $3.20 costs $0.0128 per gram, which is $1.28 per 100 g.
Where a unit price calculator helps
Bulk versus regular sizes
Warehouse clubs and family packs are often, but not always, cheaper per unit. NIST’s unit pricing guidance gives the example of a 64-ounce ketchup bottle at 7¢ an ounce losing to a 38-ounce bottle at 6¢ an ounce. Checking takes a few seconds.
Sale prices and coupons
A sale on the small size can beat the regular price of the large one. Enter the price you’ll actually pay after the discount. The discount calculator works out sale prices, and the sales tax calculator adds tax if you want to compare final totals.
Multi-packs and counts
Paper goods, batteries, diapers and pods are sold by count. Comparing a 6-pack, a 12-pack and a 24-pack by price per item quickly shows whether the bigger pack is worth it.
Store brand versus name brand
Package sizes for store brands often differ slightly from name brands, which makes a straight price comparison misleading. Unit prices put them side by side.
Common mistakes
- Comparing ounces with fluid ounces. One is weight, the other volume. Use whichever the labels share.
- Trusting shelf tags blindly. Tags for neighboring sizes sometimes use different units, such as price per ounce next to price per pound.
- Ignoring waste. A cheaper unit price doesn’t help if a third of the bag goes stale.
- Forgetting the deal conditions. A “2 for $6” price may require buying both, so enter the combined quantity and price.
- Rounding too early. Unit prices of a few cents differ in the third decimal place, so keep the extra decimals until the end, as the calculator does.
Glossary
- Unit price: price divided by quantity in a standard unit.
- Net weight (Net Wt): the weight of the product without the packaging.
- Fluid ounce (fl oz): a US volume unit equal to 1/128 of a gallon, about 29.57 mL.
- Count (ct): the number of individual items in a package.
For other shopping maths, such as what percentage one price is of another, see the percentage calculator.
Worked examples
Small jar or big jar of peanut butter
A 16 oz jar for $3.49 against a 40 oz jar for $5.79.
Inputs: Item 1 price = $3.49; Item 1 size = 16; Item 1 unit = Ounces (weight, oz); Item 2 price = $5.79; Item 2 size = 40; Item 2 unit = Ounces (weight, oz)
Item 1: $3.49 ÷ 16 oz = $0.218/oz Item 2: $5.79 ÷ 40 oz = $0.145/oz Saving: ($0.218 − $0.145) ÷ $0.218 × 100 = 33.6%
Answer: Item 2 is the best value at $0.145/oz, 33.6% cheaper per unit than item 1.
Mixed units: pounds and ounces of coffee
Coffee in three sizes: 12 oz for $9.99, a 2 lb bag for $24.50 and 20 oz for $15.49.
Inputs: Item 1 price = $9.99; Item 1 size = 12; Item 1 unit = Ounces (weight, oz); Item 2 price = $24.50; Item 2 size = 2; Item 2 unit = Pounds (lb); Item 3 price = $15.49; Item 3 size = 20; Item 3 unit = Ounces (weight, oz)
Item 1: $9.99 ÷ 12 oz = $0.833/oz Item 2: $24.50 ÷ 32 oz (2 lb) = $0.766/oz Item 3: $15.49 ÷ 20 oz = $0.775/oz Saving: ($0.833 − $0.766) ÷ $0.833 × 100 = 8%
Answer: Item 2 is the best value at $0.766/oz, 8% cheaper per unit than item 1 (1.1% cheaper than item 3).
Paper towels by the roll
Rolls sold as a 6-pack ($8.99), a 12-pack ($17.49), a single roll ($1.79) and two dozen ($27.99).
Inputs: Item 1 price = $8.99; Item 1 size = 6; Item 1 unit = Count (items); Item 2 price = $17.49; Item 2 size = 12; Item 2 unit = Count (items); Item 3 price = $1.79; Item 3 size = 1; Item 3 unit = Count (items); Item 4 price = $27.99; Item 4 size = 2; Item 4 unit = Dozen
Item 1: $8.99 ÷ 6 ct = $1.50/ct Item 2: $17.49 ÷ 12 ct = $1.46/ct Item 3: $1.79 ÷ 1 ct = $1.79/ct Item 4: $27.99 ÷ 24 ct (2 dozen) = $1.17/ct Saving: ($1.79 − $1.17) ÷ $1.79 × 100 = 34.8%
Answer: Item 4 is the best value at $1.17/ct, 34.8% cheaper per unit than item 3 (22.2% cheaper than item 1, 20% cheaper than item 2).
Edge case: identical unit prices
A 1 L bottle at $2.50 and a 2,000 mL bottle at $5 cost exactly the same per liter.
Inputs: Item 1 price = $2.50; Item 1 size = 1; Item 1 unit = Liters (L); Item 2 price = $5; Item 2 size = 2000; Item 2 unit = Milliliters (mL)
Item 1: $2.50 ÷ 1 L = $2.50/L Item 2: $5.00 ÷ 2 L (2,000 mL) = $2.50/L
Answer: All items cost $2.50/L.
Assumptions and limitations
- Every item is converted to the unit chosen for item 1, using exact definitions (1 lb = 16 oz, 1 oz = 28.349523125 g, 1 US gallon = 128 fl oz = 3.785411784 L, 1 dozen = 12).
- All items must be measured the same way, by weight, by volume or by count. Ounces (oz) are weight and fluid ounces (fl oz) are volume, so they can't be compared directly.
- The saving is (most expensive unit price − cheapest unit price) ÷ most expensive unit price × 100, the percentage less you pay per unit by choosing the cheapest item.
- Unit prices under $1 are shown to 3 or 4 decimal places so close prices can be told apart. Items whose unit prices round to the same figure are treated as equal.
- Prices are taken as entered. Coupons, multi-buy deals, sales tax and deposits aren't applied unless you include them in the price.
Frequently asked questions
How do you calculate unit price?
Divide the price by the quantity. A 24 oz jar for $5.04 costs 5.04 ÷ 24 = $0.21 per ounce. To compare packages, make sure every quantity is in the same unit first.
How do I compare prices when one item is in pounds and the other in ounces?
Convert both to the same unit. One pound is 16 ounces, so a 3 lb bag is 48 oz. The unit price calculator does this for you when you choose a different unit for each item.
Is the bigger package always cheaper per unit?
Usually, but not always. NIST's unit pricing guidance gives the example of a 64-ounce bottle of ketchup at $4.49 (7¢ an ounce) costing more per ounce than a 38-ounce bottle at $2.29 (6¢ an ounce). Checking the unit price is the only way to be sure.
What is the difference between ounces and fluid ounces?
An ounce (oz) measures weight, and a fluid ounce (fl oz) measures volume. They're only roughly equal for water-like liquids, so compare dry goods by weight and drinks by volume, as printed on the label.
How do I compare multi-packs and single items?
Use count. Enter each pack's price with the number of items in it, such as 12 rolls or 2 dozen eggs, and the calculator gives the price per item.
Should I always buy the cheapest unit price?
Only if you'll use it all. A bigger pack that spoils or expires before you finish it costs more per unit actually used. Storage space and cash flow matter too.
Sources
- Unit Pricing Guide (NIST Special Publication 1181) — National Institute of Standards and Technology. Checked October 10, 2026.
- New Best Practices Guide Shows Unit Pricing Is a Great Deal — National Institute of Standards and Technology. Checked October 10, 2026.
- NIST Handbook 130 - Current Edition (Uniform Unit Pricing Regulation) — National Institute of Standards and Technology. Checked October 10, 2026.