Unit Price Calculator
Unit price is the price divided by the amount you get, written per ounce, pound, liter or item so different sizes can be compared. In the example, Gallon jug ($3.79 for 1 gal), 12-pack cans ($6.49 for 12 × 12 fl oz) and 2 L bottle ($1.89 for 2 L) come to $0.0296, $0.0451 and $0.0279 per fl oz. 2 L bottle is the best value at $0.0279 per fl oz. The next cheapest, Gallon jug, costs 5.9% more per fl oz; the dearest, 12-pack cans, costs 61.3% more. Choosing the best over Gallon jug saves 5.6% per fl oz. Enter each product’s price, its size and unit, and a multipack count if there is one; the calculator converts every row to one common unit, ranks them from cheapest to most expensive, and shows how much more each costs than the best value. Money is exact to the cent and unit conversions use the NIST definitions. A row measured by weight is never converted to volume or the other way round: it is flagged instead.
Updated Runs in your browser: nothing you enter is uploadedHow this tool works
2 L bottle is the best value at $0.0279 per fl oz
The next cheapest, Gallon jug, costs 5.9% more per fl oz; the dearest, 12-pack cans, costs 61.3% more. Choosing the best over Gallon jug saves 5.6% per fl oz.
Volume, compared per fl oz
- Rank 12 L bottleBest value
$0.0279 per fl oz
- 5.6% less per fl oz than Gallon jug
- 38.0% less per fl oz than 12-pack cans
- Rank 2Gallon jug
$0.0296 per fl oz
5.9% more than the best value
- 34.3% less per fl oz than 12-pack cans
- Rank 312-pack cans
$0.0451 per fl oz
61.3% more than the best value
- Unit prices are shown per fl oz, the unit most rows already use. Pick another unit to change it.
- A fluid ounce here is the US fluid ounce (1/128 US gallon); a weight ounce is a different unit.
The example comparison, cheapest first
| Rank | Product | Price | Amount | Unit price | Compared with the best |
|---|---|---|---|---|---|
| 1 | 2 L bottle | $1.89 | 2 L (≈ 67.628 fl oz) | $0.0279 per fl oz | Best value |
| 2 | Gallon jug | $3.79 | 1 gal (128 fl oz) | $0.0296 per fl oz | 5.9% more |
| 3 | 12-pack cans | $6.49 | 12 × 12 fl oz (144 fl oz) | $0.0451 per fl oz | 61.3% more |
One price, many units
| Per | Unit price |
|---|---|
| Fluid ounce (fl oz) | $0.0296 |
| Cup (cup) | $0.237 |
| Quart (qt) | $0.948 |
| Gallon (gal) | $3.79 |
| Milliliter (mL) | $0.00100 |
| Liter (L) | $1.00 |
Exact conversion factors used
| Unit | Equals |
|---|---|
| Ounce (oz) | 28.349523125 g |
| Pound (lb) | 453.59237 g |
| Kilogram (kg) | 1,000 g |
| Fluid ounce (fl oz) | 29.5735295625 mL |
| Cup (cup) | 236.5882365 mL |
| Pint (pt) | 473.176473 mL |
| Quart (qt) | 946.352946 mL |
| Gallon (gal) | 3,785.411784 mL |
| Liter (L) | 1,000 mL |
How to compare products by unit price
- Enter the first product. Type its price and the size printed on the label, and pick the unit. The first example row is $3.79 for 1 gal. The product name is optional and only used to label the result.
- Add a multipack count if there is one. For a pack of 12 cans of 12 fl oz, enter 12 as the quantity, fl oz as the unit and 12 as the multipack: the calculator multiplies them to 144 fl oz. Leave the multipack blank for a single item.
- Add the other products. Add a row for each product you are choosing between. Units can differ: gallons, fluid ounces and liters in the same list are all converted exactly. Rows left empty are ignored.
- Choose the unit to compare per. “Automatic” uses the unit most of your rows already use. Choose another, such as liters, and every volume row is shown in it: the example’s best value becomes $0.945 per L.
- Read the ranking. The cheapest row is highlighted as the best value and the rest are listed from cheapest to most expensive with the percentage each costs more. 12-pack cans costs 61.3% more per fluid ounce here.
Frequently asked questions
- How do I calculate unit price?
- Divide the price by the amount. $3.79 for a gallon (128 US fluid ounces) is $3.79 ÷ 128 = $0.0296 per fluid ounce. To compare products sold in different sizes, work out the unit price of each in the same unit; the calculator converts the units and does the division for every row.
- How do I compare a multipack with a single bottle?
- Multiply the pack by the size of each item and divide the price by that. A $6.49 pack of 12 × 12 fl oz holds 144 fl oz, which is $0.0451 per fl oz. Enter the number of items in the multipack field and the size of one item as the quantity.
- Is the bigger size always the cheaper one?
- No. In the example the gallon jug is the larger container (128 fl oz), but the 2 L bottle (≈ 67.628 fl oz) is cheaper per fluid ounce: $0.0279 against $0.0296, so the jug costs 5.9% more than the best value. Always compare the unit price, not the package size.
- Why does the calculator refuse to compare weight and volume?
- An ounce of weight and a fluid ounce of volume measure different things, and turning one into the other needs the product’s density (a fluid ounce of honey weighs far more than one of oil). A shelf label does not give it, so the calculator never guesses. Add a flour row priced by the pound to the example and it is flagged: “Can’t be compared: it is the only weight row and the others are priced by volume.” Rows are compared only with others measured the same way.
- What is the difference between oz and fl oz?
- Ounce (oz) is a unit of weight, 1/16 of a pound. Fluid ounce (fl oz) is a unit of volume, 1/128 of a US gallon, about 29.57 mL. They are different units with a similar name, and a package of a liquid is often labelled with its volume while a dry food is labelled with its weight. The calculator treats them as different kinds of unit, so it never mixes them up.
- Which fluid ounce and gallon does it use?
- The US fluid ounce and US gallon: 1 US gallon is exactly 231 cubic inches (3.785411784 liters) and a fluid ounce is 1/128 of that, 29.5735295625 mL. The UK imperial gallon (4.54609 liters) and imperial fluid ounce are different and are not offered here.
- How are the unit conversions defined?
- From the definitions in NIST Handbook 44 (Appendix C) and NIST Special Publication 811 (Appendix B), not from rounded tables: 1 inch is exactly 2.54 cm, 1 pound exactly 0.45359237 kg, 1 ounce exactly 1/16 pound, and the US gallon exactly 231 cubic inches. The factors come from the same table the unit converter on this site uses.
- What is unit pricing regulation and does it apply to me?
- NIST Handbook 130 includes a model Uniform Unit Pricing Regulation that sets out how stores should show a unit price on the shelf so that shoppers can compare packages. It is a model: each state decides whether to adopt it, in what form, and which stores it covers, and many retailers show a unit price whatever the rule. This page does the arithmetic and is not legal advice; check your state’s weights and measures office for the rule where you shop.
- How exact are the numbers?
- Prices are kept in whole cents and every quantity, conversion factor and unit price is an exact fraction, so there is no floating-point error. A unit price is rounded only when it is written down, half up, to the cent or, for small prices like $0.0279, to three significant digits. Rows that differ by less than the written precision are still ranked by their exact values; two rows with exactly equal unit prices are shown as tied (for example, “Small and Large tie for best value at $0.20 per oz”).
- Can I compare weights in different units?
- Yes. A 1 lb bag, an 8 oz box and a 1.5 kg bulk pack are each converted to one unit (per oz) and ranked: Bulk is the best value at $0.189 per oz. Length, area (square feet) and count (each) work the same way.
- Is anything I type stored or sent?
- No. The calculation runs in your browser and nothing you enter leaves your device.
How it works
Each row’s price is read as whole cents (more than two decimals are rounded half up to the cent). Its total amount is the quantity times the multipack count, in the row’s own unit. Each unit has an exact factor to its dimension’s base unit (kilogram for weight, cubic meter for volume, meter for length, square meter for area, one item for count), taken from the unit converter’s table, which writes them from their NIST definitions. The total is converted to the common unit by multiplying by the row’s factor and dividing by the common unit’s factor, in exact fractions. The unit price is the price in cents divided by that converted amount. Rows are grouped by what they measure and only rows in the same group are converted and ranked; the group with the most rows is shown first. The common unit is the one you pick, or else the unit most rows in the group use, with ties going to the unit listed first (ounce before pound, fluid ounce before liter). Rows are ranked from the lowest exact unit price, and equal prices share a rank. “More than the best” is the difference from the best unit price divided by the best unit price; the saving is that difference divided by the row’s own unit price, so the two percentages differ: paying 25% more than the best means the best saves 20%. Percentages are rounded to one decimal, half up. A unit price is shown with at least two decimals and as many more as it takes to show three significant digits. Fluid ounces and gallons are US customary units. The calculator uses the price as given and does not account for sales tax, deposits, coupons, loyalty prices, or differences in quality or in how much of a product you will actually use. The NIST Handbook 130 Uniform Unit Pricing Regulation is a model rule that states adopt on their own terms. Everything runs in your browser and nothing you type is sent anywhere.
Sources
- NIST Special Publication 811 (2008), Guide for the Use of the International System of Units, Appendix B: conversion factors
- NIST Handbook 44 (current edition), Appendix C: General Tables of Units of Measurement
- NIST Handbook 130, Uniform Laws and Regulations in the areas of Legal Metrology and Engine Fuel Quality: the model Uniform Unit Pricing Regulation (states adopt it, or their own version, individually)
- Unit pricing, Wikipedia
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