How to Calculate a Unit Price

Unit price makes packages of different sizes comparable by reducing each one to the cost of a single unit. Divide the price by the quantity.

$p$ is the price, $q$ is the quantity and $u$ is what one unit costs. Because a single gram or millilitre usually costs a fraction of a coin, the price per 100 units, $100u$, is shown as well.

Example

A pack priced at 298 holding 500 units gives $u = 298 \div 500 = 0.596$ per unit. For a 500 g bag, that is 0.596 per gram, or 59.6 per 100 g.

Notes

The better buy is the one with the smaller unit price, which is not always the one with the smaller price on the shelf.

Use the same unit of quantity for both products. A kilogram is 1000 grams and a litre is 1000 millilitres, so entering one pack in grams and the other in kilograms leaves the two answers a factor of 1000 apart.

A quantity of 0 leaves nothing to divide by, so no unit price exists.

A low unit price is only a saving if you use what you buy. A bulk pack that goes stale before you finish it costs more per unit actually eaten than the small pack you get through.