Unit-price comparison
Compare two pack prices on the same item, mass or liquid-volume basis and see exactly which offer is cheaper — or whether they tie.
Enter a positive whole number of items for each pack.
Use the same currency for both prices. No currency is selected, inferred or converted.
- Offer A normalized price
- $0.375 / item
- Offer B normalized price
- $0.333333 / item
- Difference at the comparison quantity
- $0.041667 / item
- Offer A price at Offer B quantity
- $6.75
- Offer B price at Offer A quantity
- $4
The comparison uses unrounded normalized prices. It does not account for quality, wastage, tax, discounts or different currencies.
Included
- Two offers priced in the same currency
- Whole item counts, metric and avoirdupois mass, and metric or U.S. liquid volume
- Unrounded unit normalization, tie detection and saving relative to the more expensive offer
- Equivalent cost of each offer at the other offer's pack quantity
Not included
- Currency conversion, tax, coupons, deposits or membership fees
- Quality, nutrition, serving size, wastage or purchase recommendations
- Dry-volume and Imperial fluid measures
- Density-based conversion between mass and volume
What this means
A larger pack is not automatically better value. The calculator converts each net amount to a shared base unit, divides price by that amount, then presents both offers at the same familiar comparison quantity.
The percentage saving is measured against the more expensive unit price. A result of 12% cheaper means the better offer costs 12% less for the same quantity, not that the whole pack price is 12% lower.
Exactly equal normalized prices are shown as a tie. Calculations use unrounded values; display rounding never decides the winner.
Formula & worked example
base amount = entered amount × exact unit factor base unit price = entered price ÷ base amount comparison price = base unit price × comparison quantity saving % = (higher base unit price − lower base unit price) ÷ higher base unit price × 100
$4.50 for 12 items compared with $6.00 for 18 items
- Offer A per item: $4.50 ÷ 12
- $0.375
- Offer B per item: $6.00 ÷ 18
- $0.333333…
- Saving relative to Offer A: ($0.375 − $0.333333…) ÷ $0.375
- 11.111111…%
Offer B is about 11.111111% cheaper per item. At 18 items, Offer A's unit price would cost $6.75.
How this calculation works
The calculation follows the formulas, definitions and assumptions explained on this page. The references below support the method and any stated boundaries.
Official sources
- NIST SP 811 — Guide for the Use of the International System of Units — Appendix B conversion factors for SI and U.S. customary mass and liquid-volume units
- NIST Handbook 44 — 2026 edition — Appendix C general conversion tables and U.S. liquid-measure relationships