How Supermarkets Use Unit Pricing to Confuse You — and How to Fight Back

Unit Pricing Was Supposed to Be the Solution

In the 1970s, consumer advocates pushed hard for mandatory unit pricing — the requirement that retailers display the price per standard measure alongside the shelf price. The logic was simple: if every product shows price per 100g or per litre, consumers can compare instantly and make informed choices. In much of the EU and Australia, this is now law. In the US, it varies by state.

It worked — partially. Unit pricing did improve consumer decision-making in controlled studies. But retailers, faced with a regulation designed to aid price comparison, proved remarkably creative in finding ways to comply with the letter of the law while undermining its spirit.

The Legal Landscape

EU and UK

Under EU Directive 98/6/EC (retained in UK law post-Brexit), retailers must display the selling price and the price per unit of measurement for most pre-packaged goods. The unit must be meaningful — per kg, per litre, per metre — and must be displayed prominently. In practice, "prominently" is loosely interpreted and enforcement is inconsistent. Supermarkets are rarely penalised for unit price labels that are technically present but practically invisible.

United States

The US has no federal unit pricing law. State laws vary significantly: Massachusetts and New York have mandatory requirements for large retailers; most other states have voluntary programmes or no requirement at all. Even where unit pricing is displayed, the unit used is not standardised — you may see price per ounce, per pound, or per count on adjacent shelves in the same store.

Australia

Australia's Unit Pricing Code (2009) applies to large grocery retailers and requires consistent unit pricing for pre-packaged products. The ACCC conducts compliance reviews, and Australia is generally considered one of the better-performing jurisdictions — though compliance audits still find significant rates of non-compliance.

How Retailers Undermine Unit Pricing

Inconsistent units within the same category

This is the most effective trick and the most common. On a single shelf of washing detergent, you might find one product priced per 100ml, another per wash, and a third per 100g. These units are not directly comparable — a consumer cannot quickly determine which product is cheaper without doing additional calculations. Legally, each individual label may be correct. Together, they make comparison meaningless.

Small fonts and awkward placement

Unit prices are typically displayed in a smaller font than the selling price, often in grey or light text on a pale background. On shelf-edge labels, the unit price may be in 6pt type while the selling price is in 24pt type. Regulations specify that unit prices must be "legible" but rarely specify minimum font sizes. Older shoppers and those with visual impairments are disproportionately disadvantaged.

Placement matters too. On multi-tiered shelves, the unit price label for items on the bottom shelf may be at ankle height — technically present, practically invisible unless you crouch down to read it.

Shrinkflation

Shrinkflation is the practice of reducing package size while maintaining the price — and, crucially, maintaining the appearance of the product. A chocolate bar shrinks from 200g to 175g. A tube of toothpaste goes from 100ml to 90ml. Prices stay the same. The effective price per unit rises by 11–14%, but because the sticker price is unchanged, most consumers don't notice.

The Office for National Statistics in the UK has tracked shrinkflation across hundreds of products. In periods of high input cost inflation (2021–2023), shrinkflation was widespread across food, confectionery, personal care, and household cleaning products. Unit pricing should, in theory, expose this — but only if consumers are actually reading it.

Promotional pricing that obscures unit comparison

"2 for £5" promotions often display the promotional price prominently while omitting or reducing the visibility of the per-unit price during the offer. The effective unit price of the offer may be worse than the regular unit price of a competing product — but the visual emphasis on the promotional mechanic makes this hard to see.

Strategies for Fighting Back

Always compare the same unit type

If unit prices are shown in different measures within the same category, convert them yourself. Divide price by weight or volume to get a common denominator. A price per unit calculator does this instantly — enter price and quantity for each product and compare directly.

Know your anchor prices

For the 10–15 products you buy most regularly, memorise a rough benchmark price per unit. When your usual pasta is £0.18/100g, you'll instantly recognise that a "special offer" at £0.22/100g is not actually a deal. Anchoring to unit prices rather than pack prices makes deals and tricks visible without mental effort.

Use your phone

The supermarket relies on time pressure and cognitive load to prevent careful comparison. Removing the time pressure — taking a moment to calculate on your phone — defeats the strategy entirely. A basic division takes five seconds.

Weigh products where legal

In produce sections with in-store scales, use them. "Loose" produce often carries per-kg pricing that is genuinely easier to compare than pre-packaged options. The transparency is usually better because there's no packaging to obscure the quantity.

Supermarkets are sophisticated retail environments designed by experts in consumer psychology. Unit pricing law was intended to level the playing field — but compliance without intent leaves consumers still needing to be actively vigilant. The tools exist. Using them consistently is what separates informed shopping from expensive guesswork.