Home / Everyday / Unit Price Calculator
Unit Price Calculator: Which Pack Is the Best Value?
Enter the price and size of up to four products to compare them on one common basis, such as price per kilogram or per litre. Pack sizes in different units are converted, and the cheapest option is highlighted.
How unit prices are compared
A unit price is the price divided by the quantity, expressed on a common basis. Comparing a 400 g pack with a 1 kg pack is only possible once both are in the same unit. The calculator converts every quantity to grams, millilitres or a count, divides the price by it, and then scales the result to the unit you chose to compare.
Price per kg = price ÷ quantity in kg
With the default packs, 3.50 for 400 g is 8.75 per kg, 8.40 for 1 kg is 8.40 per kg, and 5.20 for 500 g is 10.40 per kg. The 1 kg pack is cheapest; the 400 g pack costs about 4.2% more per kg, and the 500 g pack about 23.8% more.
Units used for conversion
| Unit | Exact definition |
|---|---|
| 1 ounce (weight) | 28.349523125 g |
| 1 pound | 453.59237 g |
| 1 US fluid ounce | 29.5735295625 ml |
| 1 US gallon | 3,785.411784 ml |
Weight and volume cannot be compared with each other, because the conversion depends on density. The calculator therefore checks that every product uses the same kind of unit as the basis you picked, and shows a message if a pack in millilitres is compared against a price per kilogram. Imperial fluid ounces and pints differ from the US ones, so convert those to millilitres before entering them.
What unit prices do not tell you
- Waste. A larger pack is only cheaper if you use all of it. Fresh food that spoils turns a lower unit price into a higher real cost.
- Concentration and strength. Concentrated products may need dilution, so compare the cost per use, not per volume.
- Multipacks. Enter the total quantity, not the size of one item, or the comparison will be wrong.
- Drained weight and packaging. Some products state the net weight with liquid. Use the figure the label gives for the food itself.
- Quality and storage. Cost per unit ignores taste, ingredients and the space and cash tied up in bulk.
Shelf labels may already show a unit price, but they sometimes use different bases for different products. Calculating your own removes that mismatch.
Limits
The tool compares up to four products at a time and rounds displayed figures, while the ranking uses unrounded values. Prices are generic amounts in whatever currency you use, and discounts such as buy-one-get-one-free should be entered as the effective total price for the total quantity you receive. To work out a percentage saving between two prices, the percentage calculator is useful.
Worked example
Three packs of the same food: 400 g for 3.50, 1 kg for 8.40 and 500 g for 5.20. Prices are compared per kilogram even though the packs are labelled in different units.
Result
8.4000 per kg.
| Cheapest option | Product B |
|---|---|
| Price per kg | 8.4000 |
| Products compared | 3 |
Price per kg for each product
| Product | Price | Size | Per kg | More than cheapest |
|---|---|---|---|---|
| Product A | 3.50 | 400 g | 8.7500 | +4.2% |
| Product B (cheapest) | 8.40 | 1 kg | 8.4000 | - |
| Product C | 5.20 | 500 g | 10.4000 | +23.8% |
- The cheapest unit price is not always the best choice. Consider whether you will use the whole pack before it spoils, and the quality of the product.
Accuracy note: Results are calculated in your browser from the values you enter. Check anything that matters for legal, academic or financial purposes against the official source.
Frequently asked questions
How do I calculate the unit price of a product?
Divide the price by the quantity in the unit you want to compare. For example, 3.50 for 400 grams is 0.00875 per gram, or 8.75 per kilogram.
Is the bigger pack always cheaper per unit?
Not always. Some larger packs cost more per unit than smaller ones, especially when a smaller pack is on promotion. That is why it is worth calculating rather than assuming.
Can I compare products sold in different units?
Yes, as long as they measure the same kind of thing. You can compare grams with ounces or millilitres with litres, but not weight against volume.
How should I enter a multipack?
Enter the total quantity across all the items. Six cans of 330 millilitres is 1,980 millilitres, or 1.98 litres, entered with the total price of the pack.
How do I handle a buy-one-get-one-free offer?
Enter the price you pay as the price and the quantity of everything you receive as the quantity. Two packs for the price of one halves the unit price.