About the Unit Price calculator
Is the big box really cheaper than the small one? This unit price calculator compares two products by working out the price per unit for each, such as per ounce, per pound, per liter or per item. It then tells you which is the better deal and by what percentage.
Shelf tags don't always show unit prices, and when they do, the two items may use different units. Entering the price and size of each item here gives a fair, side-by-side comparison in seconds.
How to use it
- Enter the Item A price and Item A size.
- Enter the Item B price and Item B size.
- Type the Size unit for both items, such as oz, lb, L or items.
- Read each item's price per unit and which one is the better deal.
The formula
The unit price is the price divided by the amount you get:
unit price = price ÷ size
The better deal is the lower unit price. The saving is shown as a percentage of the more expensive unit price:
% cheaper = (higher unit price − lower unit price) ÷ higher unit price × 100
- Both sizes must be in the same unit. The Size unit box only labels the result; it doesn't convert anything.
- Unit prices are shown to four decimal places, because small differences add up on cheap items.
Worked example
A 16 oz jar of peanut butter costs $4.99 and a 28 oz jar costs $7.49.
- Item A: $4.99 ÷ 16 = $0.3119 per oz
- Item B: $7.49 ÷ 28 = $0.2675 per oz
Item B is the better deal, 14.2% cheaper per ounce. If you'll use it all before it goes stale, the bigger jar saves money.
Here's another way to think about it: buying 28 oz in 16 oz jars would cost 28 × $0.3119 = $8.73, so the big jar saves about $1.24.
Smart comparison tips
Match the units. If one item is in ounces and the other in pounds, convert first. 1 lb = 16 oz. For metric and US sizes, use the weight converter or the volume converter. Remember that fluid ounces measure volume and ounces measure weight.
Multipacks. For a 12-pack of 500 mL bottles, use 12 items, or 6 liters, as the size. For products sold by count, such as diapers, batteries or tablets, "per item" is often the fairest comparison.
Bigger isn't always cheaper. Sale prices and coupons on smaller sizes can make them the better buy, so compare with the actual price you'll pay. To work out a sale price first, use the discount calculator.
Waste counts. A lower unit price only saves money if you use the whole thing.
Frequently asked questions
How do I calculate unit price?
Divide the price by the quantity. A $6 pack of 24 items costs $6 ÷ 24 = $0.25 per item.
Is the bigger package always cheaper per unit?
Often, but not always. Sales, coupons and store-brand pricing can make a smaller package cheaper per unit, so it's worth checking.
What if the two products use different units?
Convert one to match the other before entering the sizes. For example, 2 lb is 32 oz. The calculator doesn't convert units for you.
How do I compare multipacks?
Use the total amount in the pack as the size, such as 12 cans × 12 fl oz = 144 fl oz, or simply the number of items.
What does the percentage cheaper mean?
It's how much less the cheaper item costs per unit, compared with the more expensive one. 14% cheaper means you pay 14% less for the same amount.
Last updated October 24, 2026. Results are estimates for education and planning — see our disclaimer.