How to use the unit price calculator
- Type each item's price and size as printed on the pack, and pick the unit: oz, lb, g, kg, fl oz, ml, L or items. You can compare 2 to 6 items.
- For a multipack, type the number of units in Pack of and the size of one unit: a 6 pack of 12 fl oz cans is Pack of 6, size 12, fl oz.
- Read the result. Each item shows its price per unit, the best value is labeled Best value and named at the top, and the line below says how much you save.
Items can use different units of the same kind, such as ounces and grams. Change Show price per to see every item per ounce, per pound, per 100 grams or per kilogram (or per fluid ounce, per 100 ml or per liter).
How to calculate unit price
The unit price is the price divided by the quantity:
unit price = price ÷ quantity
The item with the lowest unit price is the better buy. For the saving, the calculator prices the better item's quantity at the other item's unit price and takes the difference. Which is the better buy, a 12 oz box of cereal for $3.60 or a 20 oz box for $5.00?
| Item | Price | Size | Price per ounce |
|---|---|---|---|
| Small box | $3.60 | 12 oz | 3.60 ÷ 12 = $0.30 |
| Large box | $5.00 | 20 oz | 5.00 ÷ 20 = $0.25 |
The large box costs $0.05 less per ounce, which is 16.7% less. 20 oz at the small box's price per ounce would cost 20 × $0.30 = $6.00, so the large box saves $1.00 on that amount.
Price per ounce, per 100 g and per ml: comparing different units
To compare a pack in ounces with one in grams, the calculator converts both to the same unit first. It uses the exact factors in NIST Handbook 44, whose tables give the avoirdupois ounce as 28.349 523 125
grams and the pound as 453.592 37 grams (exactly)
. For liquids, the US gallon is 231 cubic inches (exactly)
and 128 U.S. fluid ounces (exactly)
, which makes 1 US fluid ounce exactly 29.5735295625 ml.
| Unit | Equals |
|---|---|
| 1 ounce (oz) | 28.349523125 g |
| 1 pound (lb) = 16 oz | 453.59237 g |
| 1 kilogram (kg) | about 35.274 oz |
| 1 US fluid ounce (fl oz) | 29.5735295625 ml |
| 1 liter (L) | 1,000 ml, about 33.814 fl oz |
Example: a 16 oz jar of peanut butter for $4.00 against a 500 g jar for $4.50. 16 oz is 453.59 g, so the first jar is $0.882 per 100 g and the second is $0.900 per 100 g. Per ounce that is $0.250 and $0.255. The 16 oz jar is the better buy by 2.0%, and 16 oz at the 500 g jar's rate would cost $4.08, so it saves $0.08.
Weight and volume cannot be compared. Ounces (oz) measure weight and fluid ounces (fl oz) measure volume. How much a fluid ounce weighs depends on the product, so the calculator will not compare an item in oz with one in fl oz, ml or L. It says so in words and shows each item's own unit price instead.
Multipacks and price per item
For a pack of N, the quantity is N × the size of one unit. A 6 pack of 12 fl oz cans for $4.50 holds 72 fl oz (2,129.29 ml), which is $0.211 per 100 ml. A 2 liter bottle for $2.50 is $0.125 per 100 ml, so the bottle costs 40.9% less per milliliter. 2 liters at the cans' rate would cost $4.23, so the bottle saves $1.73.
For things sold by count, such as rolls, pods or bags, pick items. 12 for $6.00 is $0.50 each and 30 for $13.50 is $0.45 each, so the pack of 30 is 10% cheaper per item and saves $1.50 on 30 items.
Unit price calculator UK: unit pricing on shelf labels
In the UK, shops must show unit prices for many goods. Article 5 of the Price Marking Order 2004 says that where a trader shows a product for sale to consumers, he shall indicate the unit price
. This applies to goods sold loose and to packs that must be marked with their quantity, with some exceptions. In the version in force from 6 April 2026, the unit price is the price for one kilogram of the product
, for one litre of the product
or for an individual item of the product
, depending on how it is sold.
So a UK shelf label often shows £ per kg or per litre. With the calculator set to kilogram, a 400 g bag for £1.20 is £3.00 per kg and a 1 kg bag for £2.75 is £2.75 per kg: the big bag is 8.3% cheaper per kilogram and saves £0.25 on 1 kg.
Unit pricing in US stores
In the US, unit pricing is set state by state, not by one national law. NIST's guide to US retail pricing laws says eighteen (18) states and one (1) territories have unit pricing laws or regulations in force
and that Ten (10) of these have mandatory unit pricing provisions.
Where a state's rules are voluntary, NIST notes that they apply only when stores voluntarily provide unit pricing information.
So a shelf tag may or may not show a unit price, and two tags in the same aisle may use different units. Working it out yourself puts every item on the same unit.
Unit price in Excel or Google Sheets
Put the price in column B and the quantity in column C, both in the same unit. In D2 type =B2/C2 and fill it down for the unit price. Then =MIN(D2:D4) gives the lowest unit price, which is the better buy. MIN works the same way in Excel and Google Sheets.
If the sizes use different units, convert them first: grams to ounces is =C2/28.349523125 and milliliters to US fluid ounces is =C2/29.5735295625.
When the cheaper unit price is not the better buy
- Waste. A big pack of something that spoils before you finish it costs more per unit you actually use.
- Sale prices. A smaller pack on offer can beat the big one. Type the price you will actually pay.
- Rounded labels. Shelf labels round the unit price, so two items can look the same. The calculator compares the exact figures.
- Different products. Unit price compares the amount, not the quality or the concentration, such as a concentrated detergent that needs less per wash.
Questions and answers
How do I calculate price per ounce?
Divide the price by the number of ounces. A 20 oz box for $5.00 is 5.00 ÷ 20 = $0.25 per ounce. If the pack is in grams, divide the grams by 28.349523125 to get ounces first.
Which is the better buy?
The item with the lower unit price, once both are in the same unit. A 16 oz jar for $4.00 ($0.250 per oz) beats a 500 g jar for $4.50 ($0.255 per oz), even though the 500 g jar is bigger.
Can I compare ounces with fluid ounces?
No. Ounces measure weight and fluid ounces measure volume, and how much a fluid ounce weighs depends on the product. Compare items measured the same way.
How many grams are in an ounce?
Exactly 28.349523125 grams in an avoirdupois ounce, the ounce used for food in US stores, according to NIST Handbook 44. A pound is exactly 453.59237 grams.
What does the unit price on a UK shelf label mean?
It is the price for one kilogram, one litre or one item of the product, so you can compare packs of different sizes. Shops must show it for many goods under the Price Marking Order 2004.
Sources
Checked on 8 October 2026. If a rule has changed, please tell us.
- NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement
- NIST: A Guide to U.S. Retail Pricing Laws and Regulations
- The Price Marking Order 2004, article 5 (legislation.gov.uk)
- The Price Marking Order 2004, article 1: definition of unit price (legislation.gov.uk)
- Microsoft Support: MIN function
- Google Docs Editors Help: MIN