Unit Price Comparison Calculator
Turn products of different sizes into one fair price per unit and see which is cheaper — and by how much.
How the comparison works
- Sizes are converted to a base unit: grams for weight, millilitres for volume and items for counts. 1 kg is 1,000 g, 1 lb is 453.59 g, 1 L is 1,000 ml and 1 US fl oz is 29.57 ml.
- The price is divided by the quantity in base units to get a unit price. Weight and volume are shown per 100 g and per 100 ml (plus per ounce or per US fl oz), and counts per item.
- The gap between the cheapest and the most expensive product is shown as a percentage of the expensive one. If product 1 costs 300 per 100 g and product 2 costs 250, that is (300 − 250) ÷ 300 ≈ 16.7% cheaper.
- If you mix units that cannot be compared — weight with volume, or either with a count — it does not compare them and tells you why. A litre of milk and 500 g of cheese cannot be put on the same line, however you convert them.
Worked examples
| What is compared | Unit price | Result |
|---|---|---|
| Milk: 900 ml for $2.30 vs 1 L for $2.60 | $0.2556 per 100 ml · $0.0756 per US fl oz $0.26 per 100 ml · $0.0769 per US fl oz | Product 1 is 1.7% cheaper |
| Rice: 5 lb for $6.99 vs 10 lb for $12.49 | $0.3082 per 100 g · $0.0874 per oz $0.2754 per 100 g · $0.0781 per oz | Product 2 is 10.7% cheaper |
| Instant noodles: 5-pack for $4.50 vs a single pack for $1.00 | $0.90 per item $1.00 per item | Product 1 is 10% cheaper |
| Snacks: 150 g for $1.80 vs a 2-for-1 deal (150 g × 2) for $3.00 | $1.20 per 100 g · $0.3402 per oz $1.00 per 100 g · $0.2835 per oz | Product 2 is 16.7% cheaper |
The numbers in the table come from the same function as the calculator on this page, so you get the same result if you enter them yourself.
What people often miss when comparing unit prices
- The bigger pack is not always cheaper. In the rice example the 10 lb bag works out cheaper per ounce than the 5 lb bag, but in the milk example the 900 ml carton ($0.2556 per 100 ml) beats the 1 L carton ($0.26 per 100 ml).
- Add freebies to the quantity. For a 2-for-1 deal, enter double the size and the price only once. If the freebie is a different item, it is not the same product and has to be judged separately.
- Price per item and price per weight are different things. Two 6-packs can hold items of different sizes, so a per-item comparison misleads. If the size is printed on the pack, enter it in grams or ounces instead.
- Think about how fast you will use it. Fresh food or anything with a short shelf life is a loss if you throw half away, however cheap per unit. A unit price only means something if you actually use the whole thing.
- Enter the price you will actually pay, not the price before discounts. A card discount or a coupon changes the money that leaves your pocket.
When this calculator helps
Use it in the supermarket aisle when the same kind of product comes in different sizes, online when you compare a multipack with a single item, or when refills and the original bottle are priced differently (detergent, shampoo, wipes). Some shops print a unit price on the shelf, but the base unit differs from shop to shop, so lining them up yourself is more reliable.
Frequently asked questions
How is the unit price calculated?
Price ÷ quantity in the base unit. For $2.30 for 900 ml that is about 0.26 cents per ml, shown as roughly $0.2556 per 100 ml to make it easier to read.
Can I compare ounces with grams, or pounds with kilograms?
Yes. Everything is converted to grams or millilitres first (1 oz = 28.35 g, 1 lb = 453.59 g, 1 US fl oz = 29.57 ml, 1 US gal = 3,785.41 ml), so mixed units are fine. Weight, volume and counts still cannot be compared with each other.
Can I compare three products?
Yes. Fill in the price and the size of Product 3 and all three are compared; leave it empty and only two are.
Are the prices I enter saved or sent anywhere?
No. The calculation happens only in your browser; nothing is sent to a server or stored.
More free tools
Add it to your home screen and it opens like an app — after the first visit it works offline too. What you type never leaves your device.