Unit pricing · 6 min read
How to Compare Grocery Prices Per Ounce
The shelf-tag method for online grocery: find the net weight, count every container, convert units, and compare pantry packs by price per ounce.
Deal calculator
Price per ounce calculator
Put two sizes on the same scale. Enter the total price for each option, the size of one container, and how many containers come in the pack.
Worked example
Worked example (illustrative prices): a 12 oz bag of ground coffee at $7.99 is $0.666 per ounce. A 2 lb (32 oz) bag at $17.49 is $0.547 per ounce. The bigger bag is about 18% cheaper per ounce — worth it if you finish 32 oz while it still tastes fresh.
How the math works
Each option’s unit price is its total price divided by (container size × number of containers), after converting to a common unit: pounds, grams, and kilograms become ounces; milliliters and liters become US fluid ounces. The saving is the gap between the two unit prices divided by the higher one.
Enter the price of the whole pack. For a case of twelve 15 oz cans at $14.88, enter 14.88, 15, 12. Entering the price of one can with a count of 12 would make the case look twelve times cheaper than it is.
Ounces are not fluid ounces
Ounces (oz) measure weight; fluid ounces (fl oz) measure volume. Olive oil is sold by fluid ounce, peanut butter by ounce. The calculator refuses to compare across the two because the answer would depend on the food’s density, which is not on the label.
When a lower unit price is not a saving
A cheaper ounce only counts if you eat the ounce. If a bigger bag will go stale, or a case of cans outlasts its best-by date, run the stock-up calculator with your real usage before buying the bigger option.