Unit Price & Grocery Comparison Calculator
Compare up to six products by price per ounce, pound, litre, sheet or any other unit. Mixed package units are converted for you, so a 16 oz jar and a 1 kg tub can be compared fairly.
Written by Suhaib Hassan. Conversion factors come from NIST Special Publication 811. Our methodology.
It converts every package to one base unit, divides the shelf price by the quantity, and ranks products by the resulting unit price.
Shelf labels use different units and pack sizes. This puts them on one scale and shows what the bigger pack really saves.
How unit price is calculated
Every package is converted to a common base unit first, then compared.
1. Normalise
Convert the package quantity to a base unit (grams, millilitres or items) using the factors in the table.
base qty = qty × factor2. Unit price
Divide the shelf price by the base quantity, then scale to the unit you want to see.
unit price = price ÷ base qty × unit factor3. Savings
Compare each unit price with the baseline (item A) to see the percentage saved per unit.
saving = 1 − (unit price ÷ baseline price)Worked examples
Illustrative prices, each checked by hand. The first is the default comparison.
Three sizes, one product
16 oz for $4.99, 32 oz for $8.49 and 64 oz for $15.99.
B: 8.49 ÷ 32 = $0.2653/oz
C: 15.99 ÷ 64 = $0.2498/oz
C saves 1 − 0.2498/0.3119 = 19.9%
Mixed units
A 1 lb bag at $3.20 against a 500 g bag at $2.10.
3.20 ÷ 453.59 = $0.00705/g
2.10 ÷ 500 = $0.00420/g
the 500 g bag is 40% cheaper per gram
Shrinkflation
A 16 oz pack becomes 14.5 oz at the same price.
= +10.34%
pack size falls by 1 − 14.5 ÷ 16 = 9.38%
How to compare unit prices
- Pick what the products are measured in: weight, volume, or a count such as sheets.
- Enter each shelf price and the net quantity printed on the package, and choose the unit that the label uses.
- Read the unit price on each card. The lowest is marked as the best buy.
- Check the bigger pack will actually be used before it expires or goes stale.
Unit price is only one part of value. A larger pack is not a saving if some of it is thrown away, and store brands can differ in quality.
By Suhaib Hassan · Reviewed 29 September 2026 · How CalculatePilot verifies formulas →
Sources
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), and NIST conversion factors for pounds, ounces, gallons and pints.
- NIST Handbook 130, Uniform Laws and Regulations in the Areas of Legal Metrology and Engine Fuel Quality, which includes a model unit pricing regulation for states to adopt.
Frequently asked questions
Are stores required to show unit prices?
It depends on the state. NIST Handbook 130 publishes a model unit pricing regulation, and some states or retailers follow it or similar rules, but there is no single US federal requirement. Where shown, the shelf label gives the price per a set unit such as an ounce or 100 sheets.
What is the difference between ounces and fluid ounces?
An ounce measures weight (about 28.35 g) and a fluid ounce measures volume (about 29.57 mL). They are not interchangeable: 16 fl oz of honey weighs roughly 22 to 24 oz. That is why this tool compares weight, volume and count separately.
How do I compare paper towels or toilet paper fairly?
Roll names such as "mega" or "double" are not standard. Compare the total sheet count, or total area, printed on the pack: price ÷ (rolls × sheets per roll). Use the Count option and enter the total sheets.
Is the bigger pack always cheaper per unit?
Not always. Bulk packs are usually cheaper per unit, but promotions, store brands and multi-buy deals can make a smaller pack the better value. That is what the comparison is for.
How is the shrinkflation percentage worked out?
If the price stays the same and the pack shrinks, the price per unit rises by old size ÷ new size − 1. A 16 oz pack that becomes 14.5 oz raises the price per ounce by 10.34%.
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