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Two Package Prices: Unit Cost & Quantity Savings

Compare two package prices on the same quantity basis and calculate the difference for the second package’s quantity.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Use the result with context

Results are estimates for planning and education. Confirm rates, taxes, fees, and legal requirements with the relevant institution or a qualified professional before making a financial decision.

Formula and method

A 4-unit package costing 12 costs 3 per unit. A 10-unit package costing 25 costs 2.5 per unit, saving 5 against buying that quantity at the first unit price.

Unit price = package price ÷ quantity; comparison cost = second quantity × first unit price; savings = comparison cost − second price

Worked example

Enter these known values and leave the other values blank.

Quantity in option 1
4
Total price of option 1
12 USD
Quantity in option 2
10
Total price of option 2
25 USD
Price per unit for option 1
3 USD / unit
Price per unit for option 2
2.5 USD / unit
Option 2 quantity at option 1 unit price
30 USD
Savings from option 2 at its quantity
5 USD

Assumptions and limitations

  • Both quantities and prices are positive. Enter comparable goods using the same quantity unit and currency.
  • Savings compare the second quantity at both unit prices. The tool does not round purchases to whole packages.
  • Quality, waste, shipping, tax differences and storage needs are outside this arithmetic comparison.

Common questions

Why can savings be negative?

The second option costs more per unit. The negative amount measures the extra cost for the second quantity.

Can I compare grams with kilograms directly?

Convert both quantities to the same unit first. These quantity fields do not perform a mass conversion.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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