How Unit Pricing Works And Where It Misleads

Unit pricing exists so that shoppers can compare products sold in different pack sizes. It is the most useful number on a shelf label and also the most frequently misapplied.

What the figure actually represents

The unit price divides the shelf price by a standard measure, giving cost per hundred grams, per litre, per sheet or per item depending on the product.

This removes pack size from the comparison entirely. Two boxes of very different volumes become directly comparable once both are expressed against the same measure.

Retailers are generally required to display it, which is why it appears in small type beneath the headline price rather than as a marketing feature.

Inconsistent measures break the comparison

The measure chosen is not always the same across a shelf. One product may be priced per hundred grams and its neighbour per kilogram, which shifts the decimal point.

Items sold both by weight and by count create the same problem. Cost per item and cost per hundred grams cannot be compared without doing arithmetic.

Promotional labels sometimes show the unit price of the pre-discount amount, or omit it entirely, which is when the most misleading comparisons occur.

Drained weight is the number that matters for tins

Tinned goods are usually labelled with both a total weight and a drained weight, since much of the contents is water or brine that gets poured away.

A unit price calculated on the total weight understates the true cost of the food. Two tins at the same headline price can differ substantially once drained.

The same effect applies to frozen products with a glaze of ice, and to meat sold in packaging that includes a marinade or added water.

Concentration changes what a litre means

Cordials, cleaning products and stock all vary in strength. Comparing them per litre compares the container rather than the number of servings it produces.

The relevant unit for a concentrate is cost per prepared serving, which requires reading the dilution instructions and doing a short calculation.

Manufacturers occasionally reduce concentration while keeping the bottle size and price constant. This is invisible in the unit price and shows up only in how quickly the bottle empties.

Cheapest per unit is not always cheapest overall

A low unit price on something that will be partly wasted is not a saving, as the arithmetic assumes the whole pack gets used.

Quality differences also survive the calculation. A cheaper product used in larger quantities to achieve the same result costs more in practice.

Unit pricing is best understood as a filter rather than an answer. It eliminates the obviously poor value quickly and leaves a shorter list to judge on other grounds.