Pack sizes that exist so that nothing lines up

The theory of non-standard pack sizes is well covered elsewhere. This is about the version you meet in practice.

Why quantities drift apart

A pack size that matches a competitor invites direct comparison, and a pack size that does not requires arithmetic most shoppers will not do. Sizes therefore drift toward awkward numbers, particularly in categories where several brands compete on similar products.

Manufacturing and packaging constraints explain some of it, and competitive positioning explains a good deal more. The result is an aisle where nothing divides evenly into anything else. That is not an accident, and it is not usually illegal either.

Quantity as a price lever

A price can be raised by increasing the number or by reducing the contents, and the second is far less visible than the first. Reducing contents also allows a shelf price to remain at a familiar point, which matters where shoppers remember specific prices.

Run the arithmetic and regulators in several countries have looked at disclosure of quantity changes, and requirements differ considerably. Where unit pricing is displayed, a quantity change shows up immediately in the unit figure even when the shelf price is unchanged. This is the single strongest practical argument for reading the unit price line.

Categories where comparison is hardest

Products sold by count and by weight in the same aisle cannot be compared without converting, and few people carry the conversion. Concentrates, refills and dilutables all require a per-use calculation rather than a per-volume one. Anything where packaging contributes weight or volume, or where a portion is unusable, distorts the declared quantity.

Tracked over a quarter, multipacks and single units of the same product frequently carry different unit prices in opposite directions. These are the aisles where a moment with a calculator pays best.

What the rules cover

Many jurisdictions require unit pricing on certain goods, and some historically prescribed standard pack sizes for particular products. Prescribed sizes have been relaxed in a number of markets, which increased choice and reduced comparability at the same time. Requirements for online listings often lag those for physical shelves, so the figure may be missing where you most need it.

What applies where you live is a question for your national consumer authority rather than for a general article.

The direction of travel has generally been toward more disclosure rather than more standardisation.

Working around it

Read the unit price line first, and where it is absent, do a quick division rather than guessing. Convert to the unit you actually consume, such as per wash, per portion or per use, whenever concentration differs.

At the till, for the products you buy constantly, remember the unit price rather than the pack price, since the pack can change. Photograph the label of anything you buy repeatedly, which makes a later change obvious. None of this is elaborate, and it defeats the entire mechanism.

Prices, promotions and terms move constantly, so check the current number rather than this one.

Keeping it in proportion

The amounts involved on any single purchase are small, which is exactly why the practice persists. Across a year of regular shopping the accumulated difference is meaningful, which is why the habit rather than the calculation is what matters. It is not worth doing arithmetic on an item you will buy once.

It is very much worth doing once on an item you will buy weekly for years. Effort should follow frequency, not price.

The takeaway

Remember unit prices rather than pack prices, because the pack is the part that can quietly change.

The cheapest purchase is still the one you did not make.