Unit Price Calculator

How to compare prices by unit

The sticker price tells you what a package costs, not what the food, detergent or shampoo inside it costs. To compare two sizes you divide each price by the amount in the package, which gives the unit price: dollars per ounce, per 100 grams, per litre or per item. The lower unit price is the better deal for the same product.

1. Enter each product’s price and the size printed on the label, with its unit.
2. Use weight units for things sold by weight (net wt), volume units for liquids, and items for counts such as eggs, rolls or pods.
3. Add a third or fourth product to compare more sizes or brands.

You can mix units within the same kind: a 16 oz jar can be compared with a 500 g jar, or a gallon with a 2-litre bottle. The calculator converts every size exactly and shows the result per ounce (or fluid ounce) and per 100 grams (or 100 mL), the units most shelf labels use in the US and in metric countries.

Unit price formula

Sizes are converted with the exact definitions of each unit:

1 oz

28.349523125 g (1/16 of the pound of 453.59237 g)

1 lb

453.59237 g

1 fl oz

29.5735295625 mL (US fluid ounce, 1/128 of a US gallon)

1 gal

3.785411784 L (US liquid gallon)

Weight and volume can’t be converted into each other without knowing the product’s density — a fluid ounce of honey weighs roughly 40% more than a fluid ounce of water — so the calculator won’t mix them. The same goes for counts: a pack of 12 isn’t a weight.

Worked example

A 16 oz jar of peanut butter costs $4.99 and a 28 oz jar costs $7.49.

1. Small jar: $4.99 ÷ 16 oz = $0.3119 per oz
2. Large jar: $7.49 ÷ 28 oz = $0.2675 per oz
3. The large jar is cheaper per ounce. The small jar costs 16.59% more per ounce, which is the same as saying the large jar is 14.23% cheaper.
4. Per 100 g: 16 oz is 453.59 g, so $1.10 per 100 g, against $0.9436 per 100 g for the large jar.

Notice the two percentages differ because each divides by a different price. “16.59% more” uses the cheaper jar as the base, “14.23% cheaper” uses the dearer one. Both are correct; the percentage calculator explains why.

When the lowest unit price isn’t the best buy

• Waste. A larger pack only saves money if you use it before it spoils or expires.
• Sales and coupons. Enter the price you would actually pay after a discount; use the discount calculator to work out a sale price and the sales tax calculator if tax applies.
• Shrinking packages. When a product gets smaller at the same price, the unit price rises even though the sticker doesn’t change. Comparing unit prices catches it.
• Shelf labels may use different units. One product may be priced per ounce and another per pound, or per count and per ounce. Enter the sizes here to put them on one scale. For a plain unit conversion, use the weight converter.