Why compare unit prices?
Shops sell the same product in many sizes, and the bigger pack is not always the better deal. Multi-buy offers, promotional sizes and imported goods labelled in ounces make comparisons even harder. The fair way to compare is the unit price: how much you pay for the same amount of product, such as one kilogram, one litre or one item. This calculator does that conversion for every option you enter and tells you which one is cheapest and by how much the others cost more.
How to use it
For each option, enter a name, the shelf price and the size of one pack with its unit. If the offer is for several packs, for example three tins for the price shown, put 3 in the Packs column. The unit price column updates as you type, the cheapest option is marked, and the others show the percentage extra you would pay for the same quantity. Add as many rows as you need with the Add option button.
How the conversion works
Every unit is converted to a base unit in the same family using exact definitions: weights to kilograms (an ounce is 28.349523125 g and a pound 453.59237 g), volumes to litres (a US fluid ounce is 29.5735 ml and a US gallon 3.785 litres), lengths to metres, areas to square metres, and counts to single items. The unit price is the total price divided by the total quantity in base units. Because weight, volume and count measure different things, the calculator will not compare across families, for example grams against millilitres, and tells you so instead of producing a misleading answer.
Shopping tips
- Many shelf labels already show a unit price, but stores sometimes use different bases (per 100 g on one label, per kg on another). Entering the raw numbers here avoids that trap.
- The cheapest per kilo is only a saving if you will use it before it spoils. Factor in waste for fresh food.
- For liquids sold by weight, such as honey, compare in grams rather than mixing units.
- Check whether a "bigger" pack really holds more; shrinkflation means sizes change quietly.
Privacy
All calculations run in your browser. Nothing you type is stored or sent anywhere.