Compare prices using the same unit
Unit price is the amount paid per one unit of quantity. Divide the product price by its quantity, then compare options using the same kind of unit—such as dollars per ounce, per pound, per litre, or per item. The shelf price alone can be misleading when package sizes differ.
Worked example
A 12-ounce package for $4.80 costs $0.40 per ounce. A 20-ounce package for $7.00 costs $0.35 per ounce, so the larger package has the lower price per ounce before any coupons, waste, or quality differences.
Make sure quantity units match before comparing; a price per ounce cannot be directly compared with a price per pound without conversion. This calculator compares the figures you enter and does not account for package quality, shelf life, waste, shipping, or discounts that are not included in the price.
Tips for accurate results
Convert both products to the same unit and compare the price per unit. A 12-ounce item at $3.60 costs $0.30 per ounce, while a 20-ounce item at $5.50 costs $0.275 per ounce, so the larger one is cheaper per ounce.
Common mistakes and limits
Bigger is not always cheaper, and a bulk item saves nothing if some of it spoils or goes unused. Package sizes sometimes shrink without a price change, so compare unit prices on each shopping trip. Quality and use rate matter as much as price.