Unit Price Calculator
Divide each price by its size to get the price per unit; the lower one is the better value. Enter both packages in the same unit and the calculator does the division and shows the percentage saved.
Answer
Better value
Package B
14.18% less per unit than package A.
Rounded for display. The working shows the exact value.
The cheaper unit price only saves money if you use the whole package before it goes off.
- A per unit
- 0.00698
- B per unit
- 0.00599
- per 100 units
- 0.70 vs 0.60
Check the work
Every line comes from the same calculation as the answer.
unit price = price ÷ size
| A per unit | 3.49 ÷ 500 | 0.00698 |
|---|---|---|
| B per unit | 5.99 ÷ 1,000 | 0.00599 |
| saving | (0.00698 − 0.00599) ÷ 0.00698 × 100 | 14.1834% |
How it works
A 500 g pack at 3.49 costs 3.49 ÷ 500 = 0.00698 per gram. A 1 kg pack at 5.99 costs 5.99 ÷ 1000 = 0.00599 per gram. The bigger pack is about 14% cheaper for every gram.
Bigger is not always cheaper. Multipacks, promotions on the small size and odd package sizes regularly flip the answer, and the unit price printed on a shelf label is sometimes per 100 g on one product and per kilogram on the one next to it.
The unit can be anything you can count or weigh — grams, fluid ounces, sheets of paper, washing loads, tablets — as long as both packages are measured the same way.
Formula
unit price = price ÷ size; saving = (higher − lower) ÷ higher × 100
The saving is measured against the more expensive unit price, so it answers “how much less do I pay per unit?”.
Worked examples
- Try these numbers
500 g for 3.49 against 1 kg for 5.99
- 3.49 ÷ 500 = 0.00698 per gram.
- 5.99 ÷ 1000 = 0.00599 per gram.
- (0.00698 − 0.00599) ÷ 0.00698 = 14.18%.
The 1 kg pack is 14.18% cheaper per gram.
- Try these numbers
Two sizes with the same unit price
- 2 ÷ 4 = 0.5 per unit.
- 5 ÷ 10 = 0.5 per unit.
Both cost 0.5 per unit, so the bigger pack saves nothing.
- Try these numbers
A 12-pack against a 24-pack
- 4.50 ÷ 12 = 0.375 per item.
- 9.60 ÷ 24 = 0.40 per item.
- (0.40 − 0.375) ÷ 0.40 = 6.25%.
The 12-pack is 6.25% cheaper per item, even though it is the smaller pack.
Inputs and results
- Price of A
- The price of the first package.
- Size of A
- How much the first package contains.
- Price of B
- The price of the second package.
- Size of B
- How much the second package contains, in the same unit.
- A per unit
- Price of A divided by its size.
- B per unit
- Price of B divided by its size.
- Saving
- How much less the cheaper package costs per unit, as a percentage.
When to use it
- Choosing between a small and a family-size pack in a shop.
- Checking whether a multipack offer actually costs less per item.
- Comparing an online bulk price with a local shop’s price.
Common mistakes
- Comparing one size in grams with another in kilograms.
- Trusting shelf labels that quote different reference amounts for neighbouring products.
- Buying the cheaper-per-unit pack and throwing part of it away.
What it does not do
- It compares two packages at a time.
- It does not convert units; enter 1 kg as 1000 if the other pack is in grams.
- It cannot judge quality, shelf life or how much you will really use.
Method and assumptions
Each unit price is the package price divided by the package size. The package with the lower unit price is reported as the better value.
The saving is the difference between the two unit prices divided by the higher one, times 100. Unit prices below 1 are shown to four decimal places because they are often fractions of a cent.
Assumptions
- Both package sizes are given in the same unit.
- The whole of either package would be used.
Edge cases
- Equal unit prices are reported as a tie with a 0% saving.
- Prices and sizes must be greater than zero.
- A free item in a multipack is handled by entering the total count and the price actually paid.
Sources and corrections
This calculator uses an elementary formula, so it needs no outside data source. The method, the rounding rules and how a reported error is corrected are set out in the site standards.
Result looks wrong?
Send the inputs you used and the answer you expected. Every report is checked against the formula and its tests, and confirmed errors are corrected in public.