Free · Everyday calculations

Two-Product Unit Price & Pack Comparison

Compare two products by price per mass, volume or item, including multipacks and the absolute difference in unit prices.

  • Formula & worked example
  • Private in your browser
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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.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

A 500 g pack priced at 4 costs 0.008 per gram. A 750 g pack priced at 5.25 costs 0.007 per gram, so option B is cheaper by 0.001 per gram.

Unit price = total price / (quantity per item × number of items); difference = |unit price A − unit price B|

Worked example

Enter these known values and leave the other values blank.

A: mass per item or pack
500 g
A: total price
4 USD
B: mass per item or pack
750 g
B: total price
5.25 USD
A: price per mass unit
0.01 USD / g
B: price per mass unit
0.01 USD / g
Absolute difference per mass unit
0 USD / g

Assumptions and limitations

  • Use one currency and the same tax, shipping and discount basis for a direct comparison. Currency conversions use captured exchange rates rather than live market rates; check the rate date shown by the calculator.
  • For a single measured pack, leave its item count at 1. For a multipack, enter the mass or volume of each included item and the number of items. Counts stay visible when changing modes so a previous multiplier is not hidden.
  • Quantities and counts must be positive; zero prices are allowed. Fractional quantities are mathematical equivalents rather than an assurance that a seller offers partial items.
  • The result compares unit cost only. Quality, usable yield, waste and whether you need the full quantity are separate considerations.
  • The absolute difference is per selected unit, not total checkout savings. Use a common output unit when visually comparing the two displayed prices.

Common questions

How do I compare three 500 g bags with a single 2 kg bag?

For option A enter 500 g and count 3 with the total price of all three. For option B enter 2 kg and count 1 with its total price.

References

Bookify compares item prices in the cheaper-option note, keeps quantity multipliers visible across modes, and accepts zero prices while rejecting negative prices. The US fluid ounce uses one 128th of the exact US liquid gallon, replacing the rounded captured reciprocal factor. The US customary cup uses one sixteenth of the exact US liquid gallon, replacing the rounded captured cup volume. Bookify replaces the captured rounded US gallon with the exact 3.785411784-liter definition.

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