Shelf prices hide the real cost of a product because packages come in different sizes. The unit price — price per ounce, per fluid ounce or per item — puts them on equal terms. This calculator compares two products side by side, converts between ounces, pounds, grams and kilograms (or fluid ounces, quarts, gallons and liters) automatically, and tells you which is cheaper and by how much.
How to use the unit price calculator
- Choose how the products are measured — by weight, by volume, or by count.
- Enter the price and size of item A, choosing its unit from the menu.
- Enter the price and size of item B. The units don't have to match — one can be in grams and the other in pounds.
Unit price formula
Savings % = (1 − lower unit price ÷ higher unit price) × 100
Weights are compared per ounce (1 oz = 28.3495 g), volumes per US fluid ounce (1 fl oz = 29.5735 mL), and counted items per item.
Worked example: cereal sizes
- Item A: $3.99 for 12 oz → 3.99 ÷ 12 = $0.3325 per oz
- Item B: $5.49 for 18 oz → 5.49 ÷ 18 = $0.3050 per oz
- Item B is cheaper by (1 − 0.3050 ÷ 0.3325) = 8.3%
If you buy this cereal every week, choosing B saves about $0.50 per 18 oz box compared with buying the same amount in 12 oz boxes.
Handy conversions for comparing
| Unit | Equals |
|---|---|
| 1 pound (lb) | 16 oz = 453.6 g |
| 1 kilogram (kg) | 35.27 oz = 2.205 lb |
| 100 grams | 3.527 oz |
| 1 US gallon | 128 fl oz = 3.785 L |
| 1 US quart | 32 fl oz = 0.946 L |
| 1 liter | 33.81 fl oz |
Smart shopping with unit prices
- Check the shelf tag. Many stores print a unit price in small type — but sometimes in different units for different sizes. Convert before you compare.
- Compare per use for concentrates. For detergent, compare price per load; for coffee, per cup brewed.
- Watch “bonus” packs. A bigger package with “20% more free” is only a deal if its unit price is actually lower.
- Factor in waste. Perishables you throw away raise the effective unit price.
Why unit prices matter
Small per-unit differences add up on items you buy every week. Saving three cents an ounce on a staple you go through at 50 ounces a month is $18 a year — on one product. Across a full grocery list, choosing the lower unit price where it makes sense is one of the simplest ways to cut spending without changing what you eat. It also exposes “shrinkflation”, when a package gets smaller while the shelf price stays the same: the unit price goes up even though the sticker doesn't.
Shopping a sale? The Percent Off Calculator shows the real discount, including stacked coupons.
Frequently asked questions
How do I calculate unit price?
Divide the price by the quantity. A $3.99 box of 12 oz costs 3.99 ÷ 12 = $0.33 per ounce. Compare that number across sizes and brands.
Is the bigger package always cheaper?
Often, but not always. Sales on smaller sizes, store brands and promotions can flip the comparison, which is why comparing the unit price beats assuming.
How do I compare grams with ounces?
Convert one to the other: 1 oz = 28.35 g and 1 lb = 453.6 g. This calculator does the conversion automatically and shows both items in price per ounce.
What about products sold by count, like paper towels?
Use the count option and enter sheets, rolls or loads. For paper towels and toilet paper, compare price per sheet rather than per roll, since roll sizes vary a lot.
Does a cheaper unit price always mean a better deal?
Only if you'll use it all. A giant jar that spoils before you finish it costs more per use than a smaller one you use up.