Unit Price Comparison Calculator
Compare two products by unit price to see which is better value. Enter each price and pack size in g, kg, ml, litres or items.
Reviewed by Dany, RightSums team · Updated
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shopping · Daily life · UK & US
Enter a name, price and quantity for two products, and pick the unit for each: grams, kilograms, millilitres, litres or items. The calculator converts both to the same base and works out the price per 100g for weights, per 100ml for liquids or per item for counts. It then names the cheaper option and says how much cheaper it is as a percentage. You can mix kg with g, or litres with ml, but not weight with volume or items. If both work out the same, it tells you so. Use it for multipacks, bigger sizes and offers where the shelf label is missing or hard to compare.
Accepted inputs
- Option A name, price, quantity and unit
- Option B name, price, quantity and unit
- Units: g, kg, ml, L or items
Outputs
- Cheaper option
- Percentage cheaper per 100g, 100ml or item
- Savings summary
How to use the Unit Price Comparison Calculator
- Enter the name, price and pack size of the first product and choose its unit.
- Do the same for the second product, using the same kind of unit: weight, volume or items.
- The calculator converts both to a price per 100g, per 100ml or per item.
- Read the verdict, which names the cheaper product and how much cheaper it is in percentage terms.
Frequently asked questions
How do I work out which pack is better value?
Compare the price per unit, not the pack price. 400g for £3.20 is 80p per 100g, and 1kg for £6.80 is 68p per 100g. The bigger pack is 15% cheaper per 100g, so it is better value if you will use it all.
How do I calculate price per 100g?
Divide the price by the weight in grams and multiply by 100. A 250g bag at £1.75 is £1.75 ÷ 250 × 100 = 70p per 100g. For kilograms, multiply by 1,000 first, so 2kg becomes 2,000g.
Is a bigger pack always cheaper?
No. Larger packs are often cheaper per unit, but not always, especially when a smaller size is on offer. For example, 500ml at 90p is 18p per 100ml, while 2 litres at £4 is 20p per 100ml, so the small bottle wins.
Can I compare a multipack with single items?
Yes, choose items as the unit for both. A 6-pack at £3.30 is 55p per item and a single at 70p is 70p per item, so the multipack is 21.4% cheaper each. You cannot compare items with grams or millilitres.
How is the percentage saving worked out?
It is the difference in unit price divided by the higher unit price. At 80p against 68p per 100g, the gap is 12p, and 12 ÷ 80 = 15%. That means the cheaper option costs 15% less per 100g, not that its pack is 15% cheaper.
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