Compare Three Packs per Unit
Compare three pack sizes at once and see which is cheapest per unit, and by how much.
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Formula
How the calculation works
Comparing three packs is three divisions followed by a minimum, but the reason to do all three at once is that the cheapest is not always the largest or the smallest. A 12-pack at 6.45, a 24-pack at 11.90 and a 48-pack at 21.50 work out to 0.54, 0.50 and 0.45 a unit, so the biggest wins here, and the gap between best and worst is 16.67%.
The percentage gap is the honest way to report the result, because a difference of nine cents a unit means very different things on a pack of 12 and a pack of 48. Expressing the saving against the dearest unit price lets two comparisons on different products be read side by side.
The non-obvious trap is that the ranking can flip with a small change. A discount on the middle pack, or a price rise on the largest, can move the winner without either unit price looking dramatically different. Computing all three at once is what makes that visible before you reach the till.
Common mistakes
- Buying the largest pack on the assumption it is cheapest, when the middle size often has the lowest unit price.
- Comparing the pack prices directly instead of the price per unit, which is meaningless when the quantities differ.
- Reading a small absolute difference as trivial. A few cents a unit compounds over a year of regular buying.
When to use it
- Use it in the aisle when three sizes of the same product sit next to each other and the shelf labels do not give a unit price.
- It is not the tool when the packs are not the same product or the units are not comparable; a unit price across different goods is a false comparison.
Worked example
A 6.45 for 12 is 0.54 each, B 11.90 for 24 is 0.50, C 21.50 for 48 is 0.45; C is cheapest, 16.67% under the dearest.
Common questions
What if I only have two packs?
For two packs use the unit price tool. Reach for this one when a third size makes the comparison worth doing at once.
Is the biggest pack always cheapest?
No. The middle size is often the best value, because the largest is sometimes priced up on the assumption that bigger means cheaper.
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