How to use the unit price calculator
- Add a row for each product you want to compare.
- Enter the price, the size and its unit (oz, lb, g, kg, fl oz, quarts, gallons, mL, litres or count).
- For multipacks, enter the size of one item and how many are in the pack.
- The best value is highlighted, and the table shows how much more each other option costs.
The formula
Unit price = Price ÷ (Size × Number in pack) 1 lb = 16 oz 1 kg = 35.274 oz 1 oz = 28.35 g 1 gal = 128 fl oz 1 qt = 32 fl oz 1 L = 33.814 fl oz
Worked example
Peanut butter comes in three options:
- 16 oz for $3.49 → 3.49 ÷ 16 = $0.218 per oz
- 32 oz for $5.99 → 5.99 ÷ 32 = $0.187 per oz
- 500 g (17.64 oz) for $2.50 → 2.50 ÷ 17.64 = $0.142 per oz — the best deal, about 24% cheaper per ounce than the 32 oz jar
Handy conversions for shopping
| Unit | Equals |
|---|---|
| 1 pound (lb) | 16 oz · 453.6 g |
| 1 kilogram (kg) | 35.27 oz · 2.205 lb |
| 100 grams | 3.53 oz |
| 1 US gallon | 128 fl oz · 3.785 L |
| 1 quart | 32 fl oz · 0.946 L |
| 1 litre | 33.81 fl oz |
| 2-litre bottle | 67.6 fl oz |
Smart shopping tips
- Read the unit price, not the sticker: shelf tags often list it in small print, but stores may use different units for similar items (per oz vs per lb).
- Check “family size” packs: bigger is usually cheaper per unit, but not always — especially when the smaller size is on sale.
- Watch shrinkflation: when a package gets smaller at the same price, the unit price goes up. Compare unit prices over time to spot it.
- Only buy in bulk what you’ll use: food that spoils before you finish it makes the cheaper unit price meaningless.
- Compare per use for things like detergent or coffee: price per load or per cup can be more useful than price per ounce.
- Store brands are often 20–30% cheaper per unit than name brands for very similar products.
Weight vs volume vs count
Products sold by weight (ounces, pounds, grams) can only be compared with other products sold by weight, and liquids sold by volume (fluid ounces, gallons, litres) with other liquids. Items like eggs, diapers, batteries or trash bags are compared by count. If you enter a mix, the calculator ranks each group separately so you never compare apples with fluid ounces.
Unit pricing rules
In the US, unit price labels are governed by state law, and many states follow the NIST Uniform Unit Pricing Regulation, which recommends consistent units such as price per ounce or per pound for similar products. In the UK and EU, retailers must show a unit price (for example per kilogram or per litre) next to the selling price for most food and household goods, which makes comparisons easier when shopping abroad.