Unit Price Comparison Calculator

Working out which of two products is actually better value is not always as simple as comparing the price on the label, especially when pack sizes differ. This calculator works out the price per unit for two products so you can see exactly which one is cheaper, and by how much.

How to use the unit price calculator

Choose the unit you are measuring in, such as grams, millilitres or individual items, then enter the price and quantity for each product. The calculator instantly shows the price per unit for both products, tells you which is cheaper, and shows the percentage saving between them.

How the calculation works

The calculator divides each product's price by its quantity to get a price per unit, then compares the two figures directly. The percentage saving is calculated as the difference between the two unit prices, divided by the higher of the two, multiplied by 100, giving you a clear sense of how much cheaper one option is relative to the other.

Worked example

Say Product A costs £2.50 for 500g, working out at £0.005 per gram, or half a penny per gram. Product B costs £4.00 for 900g, working out at roughly £0.0044 per gram. Product B is the better value here, coming in around 11.1% cheaper per gram than Product A, even though its total price is higher.

Where unit pricing matters most

Unit pricing is particularly useful for everyday groceries, toiletries and household products, where the same brand often sells several different pack sizes at once. It is also worth checking during promotions, since a “buy one get one free” deal or multipack discount can sometimes work out worse value per unit than a different size that looks less exciting on the shelf. Comparing loose or own-brand items against pre-packed branded versions is another common place where unit pricing reveals genuine savings.

Common mistakes people make

A common mistake is comparing total prices rather than unit prices, which can make a smaller, cheaper looking pack seem like better value when it is not. Another mistake is mixing up units, for example comparing a price per 100g against a price per kg without converting first, which throws the comparison off completely. It is also easy to forget that buying more than you need, even at a lower unit price, can end up wasting money if the product goes off or you simply do not use it all.

Related calculators

If you are comparing a straight percentage discount rather than pack sizes, try our discount calculator. Our percentage calculator is handy for other everyday maths, and if you are splitting a shared shop or bill, our split bill calculator can help divide the cost fairly.