Unit Price Comparison Calculator
Compare up to four package sizes by unit price — even when one is in ounces and another in pounds, grams or litres — with multipacks and coupons, and see which is the better buy and how much you save.
How it works
Unit price = (package price − coupon) ÷ (size × items per package), with every size first converted to the same unit · 1 lb = 16 oz = 453.6 g · 1 kg = 1,000 g · 1 gal = 4 qt = 128 fl oz = 3.785 L · Cheaper by = (other unit price − best unit price) ÷ other unit price
Cost per unit is the price divided by the quantity, which puts differently sized packages on the same footing. Shelf tags often make that hard: one jar is in ounces, the bulk bag in pounds, the imported brand in grams, and a multipack lists the size of one can. Enter each option in the unit printed on its package. The calculator converts them to a common unit — option A’s by default, or any unit you pick under More options — and names the cheapest. You can compare up to four options, enter the number of items in a multipack, and take a coupon off any option. It also shows how much cheaper the best one is per unit, the saving on a package of it, and, if you say how often you buy it, the saving per year. Units have to be of the same kind: weight can be compared with weight and volume with volume, but not ounces with fluid ounces. The bigger package is usually — but not always — cheaper per unit, so the comparison also catches a “value” size that is quietly worse.
Worked example
A 32 oz bottle at $4.99 costs 4.99 ÷ 32 = $0.1559 per ounce, while a 64 oz bottle at $7.49 costs 7.49 ÷ 64 = $0.1170 per ounce. The larger bottle is about 25% cheaper per ounce, saving $2.49 on 64 oz. Add a 6 lb bulk jug at $10.99: 6 lb is 96 oz, so it costs $0.1145 per ounce and becomes the best buy, 2.2% cheaper than the 64 oz bottle. With a $1.00 coupon on the 32 oz bottle, it drops to $0.1247 per ounce, still dearer than the big sizes.
Frequently asked questions
Is the bigger size always cheaper per unit?
Usually, but not always. Retailers sometimes price mid-sizes, sale items or small packs below the "family" size per unit. Comparing unit prices is the only reliable way to know, and the calculator flags when the smallest package wins.
The two items use different units — can I still compare?
Yes. Choose the unit printed on each package — oz, lb, g, kg, fl oz, quarts, gallons, mL, litres, items, feet or square feet — and the calculator converts them to one unit before comparing. Weight can only be compared with weight and volume with volume; ounces (weight) and fluid ounces (volume) are different things.
How do I compare multipacks?
Enter the size of one item, for example 12 fl oz for a can, and the number of items under More options. The calculator multiplies them, divides the package price by the total, and also shows the price per item.
Do coupons change which option is the better buy?
They can. A coupon lowers the price you pay for that package, so its unit price drops. Enter the coupon under More options; it is subtracted before the division.
Should I always buy the cheapest unit price?
Only if you will use it before it spoils and have room to store it. For perishables, a lower unit price is a false economy if part of the larger package goes to waste. Quality also matters when comparing different brands.
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This calculator is for educational purposes. Double-check important results before acting on them.