Unit Price Comparison Calculator
Enter the price and the net quantity of each package, pick the unit to compare in, and the calculator converts every package to that unit and ranks them.
Lowest Unit Price
Package 3
Lowest Unit Price ($)
0.229 per oz
Highest Unit Price ($)
0.2908 per oz
Lowest Is Cheaper per Unit Than the Highest by
21.28%
Highest Costs More per Unit Than the Lowest by
27.02%
Packages Compared
3
How it works
A unit price is the price of one unit of measure: the package price divided by the quantity it contains. Comparing unit prices rather than shelf prices shows which size or brand gives you the most product for the money.
Packages are often labelled in different units, such as 12 oz and 2 lb, or 500 mL and 16.9 fl oz. The calculator converts each package's size to the unit you choose to compare in, using the exact US legal definitions (1 lb = 16 oz = 453.59237 g; 1 US gallon = 231 cubic inches = 128 fl oz), then divides.
The package with the lowest unit price is the cheapest per unit. The percentages show how much less it costs per unit than the most expensive package, and how much more the most expensive one costs per unit than the cheapest. A package with price and size both left at 0 or blank is skipped, so you can compare two, three, four or five.
Formula
size in comparison unit = convert(size, package unit → comparison unit) ÷ multiple unit price = package price ÷ size in comparison unit cheaper by = (highest − lowest) ÷ highest more than lowest = (unit price − lowest) ÷ lowest
Example
A 12 oz package for $3.49, a 2 lb package for $7.99 and a 48 oz package for $10.99, compared per ounce: 2 lb is 32 oz, so the unit prices are $0.2908, $0.2497 and $0.2290 per oz.
The 48 oz package is cheapest per ounce. It is 21.28% cheaper per unit than the 12 oz package, and the 12 oz package costs 27.02% more per ounce than the 48 oz one; the 2 lb package costs 9.05% more.
Assumptions and limitations
- Unit price compares cost only. Whether the larger package is the better buy also depends on whether it will be used before it spoils and on storage space; the calculator does not weigh those.
- Sizes are the net quantity on the label. A weight ounce (oz) and a fluid ounce (fl oz) measure different things, so packages sold by weight cannot be compared with packages sold by volume.
- Volume units are US customary liquid measures (fl oz, pint, quart, gallon; not the dry pint or dry quart used for berries) and metric (mL, L). The comparison units follow those NIST Special Publication 1181, Unit Pricing Guide (2015), lists for weight, liquid volume and count.
- Shelf unit prices are usually rounded to the cent or tenth of a cent; this calculator shows four decimal places, so a figure can differ slightly from a store label.
- Coupons, multi-buy offers and deposits are not included unless you enter the price you actually pay.
Frequently asked questions
Is the biggest package always the cheapest per unit?
No. Larger sizes are often cheaper per unit, but not always: a smaller size on sale, or a store brand, can have the lower unit price. Converting every package to the same unit is the only way to tell.
How do I compare a price per 100 grams with a price per ounce?
Convert both sizes to one unit first. One ounce is 28.349523125 grams, so a package of 400 g is about 14.11 oz. The calculator does the conversion for you when the packages are labelled in different units.
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