Unit Price Calculator
With price of a 4.29 usd, size of a 12, price of b 7.49 usd, size of b 24, unit price comes to $0.3121 — cheaper unit price. It is reached in 4 steps, the last of which is min(unit_a, unit_b), and each one is printed on the page with its numbers filled in. The formula is the one published by NIST Office of Weights and Measures, not an approximation fitted to it.
Price per unit for two package sizes at once, so the bigger box can be checked rather than assumed — it is the cheaper one about four times in five, not five.
By Alex Seote, Built and maintains Rule Calculator · Formula and sources checked · How we check
Price of A 4.29, Size of A 12, Price of B 7.49, Size of B 24
$0.3121
Cheaper unit price for the example below. Editing a field recomputes the calculator below; this figure holds the answer the page was loaded with.
It is written into the HTML rather than drawn by a script, so a search engine reading this page without running JavaScript still finds an answer.
- A costs, per unit
price_a / size_a0.358- B costs, per unit
price_b / size_b0.312- The cheaper unit price
min(unit_a, unit_b)0.312- The dearer one costs more by
(max(unit_a, unit_b) - cheaper_unit) / cheaper_unit * 10014.553 %
Worked example
$4.29 for 12 is 35.75 cents each; $7.49 for 24 is 31.21 cents. The big box wins by 14.6% here — but it loses whenever the small one is on offer, which is the case shelf labels cannot show you because they print the regular price.
How to work it out yourself
- 1.Put both packages in the same unit before comparing. Twelve ounces against 1.5 pounds is not a comparison until one of them is converted.
- 2.Use the price you will actually pay, including any discount. Shelf unit-price labels are computed from the regular price and quietly stop being true during a promotion.
- 3.Count is a unit too: for nappies, batteries or paper towels the useful denominator is the item or the sheet, not the weight of the box.
The formula
- A costs, per unit
price_a / size_a - B costs, per unit
price_b / size_b - The cheaper unit price
min(unit_a, unit_b) - The dearer one costs more by
(max(unit_a, unit_b) - cheaper_unit) / cheaper_unit * 100
Questions people actually ask
- Is the bigger package always cheaper per unit?
- No, and the exceptions are common enough to be worth checking every time. Promotions on the small size, premium packaging on the large one, and the "family size" priced on convenience rather than volume all reverse it. This is the arithmetic that shelf labels exist to save you, and they are computed before discounts.
- Why does my answer differ from the shelf label?
- Shelf unit prices use the regular price and a standard denominator set by state weights-and-measures rules — per ounce, per 100 sheets, per pound — which may not be the one you care about. On promotion the label is simply out of date.
- What if the units are different?
- Convert first: this calculator divides price by size and cannot know that one figure is grams and the other ounces. The conversion pages on this site will do it, and getting it wrong by a factor of 28 is the usual way this comparison goes bad.
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