Decision tools built for clarity
Unit Price Calculator
Compare two shop offers by price per kilogram, litre, or piece and see which one is cheaper.
Enter the price, the quantity, and the unit of each offer, then calculate to see the unit prices and the cheaper offer.
The comparison covers price and quantity only; quality, freshness, packaging, and delivery are not compared.
Methodology
Formula or transformation
Normalizes each quantity to the base unit of its family (kilogram, litre, or piece), divides each price by its base quantity, and decides the cheaper offer and the saving from exact cross products, so equal unit prices are reported as the same.
Variables
- Price of an offer
- Quantity in an offer
- Quantity in the base unit (kilogram, litre, or piece)
- Price per base unit
- Saving of the cheaper offer as a percentage of the dearer one
Units
- Currency
- Kilogram
- Liter
- Piece
- Percent
Rounding policy
Unit prices and the saving keep canonical precision and are rounded to two decimal places for display.
Each quantity is converted to the base unit of its kind (kilogram, litre, or piece), each price is divided by that quantity, and the cheaper offer is decided from exact cross products.
Compare two shop offers by price per kilogram, litre, or piece and see which one is cheaper.
Reviewed sources
- NIST — Unit Pricing Guide: a best practice approach to unit pricing (SP 1181) Reviewed on 2026-09-21
Formula review history
-
Initial unit-pricing methodology and source review.
Reviewed 2026-09-21 for formula version unit-price-comparison-v1
Assumptions
- Inputs are interpreted using the displayed units and options.
- The calculation follows the methodology and factors listed in the sources.
Limitations
- Display rounding can hide additional decimal places.
- The calculation cannot add accuracy that is absent from the submitted inputs.
- The comparison covers price and quantity only; quality, freshness, packaging, and delivery are not compared.
Worked example
A 500 g pack for 12 costs 24 per kilogram, while a 1 kg pack for 20 costs 20 per kilogram, so the larger pack is about 16.67% cheaper per kilogram.
Frequently asked questions
Can I compare grams with kilograms?
Yes. Grams and kilograms are the same kind of unit and both convert to a price per kilogram; likewise millilitres and litres convert to a price per litre. Mass cannot be compared with volume or with pieces.
Why does the saving use the dearer offer as the base?
The saving is the difference between the two unit prices divided by the higher one, so it says how much less you pay per unit by choosing the cheaper offer.