Jämförpris: the only grocery number worth comparing

Swedish shelf labels are required to show a comparative price, the jämförpris, alongside the selling price. It is usually in small grey type under the number you are actually looking at, and it is the only figure on the label that lets you compare two products honestly.

Why the big number is the wrong one

The selling price answers “what will leave my account”. It does not answer “which of these is better value”, because the two things in front of you are rarely the same size.

This is not a trick question, and shoppers get it wrong constantly, because the arithmetic happens at the shelf under time pressure with a trolley in the way. The comparison is easy; doing it forty times in a single shop is not.

Working it out

Divide the price by the pack size, converted to a standard unit. Kronor per kilogram for solids, per litre for liquids, per piece for things counted rather than measured.

The two conversions worth memorising are that grams to kilograms means dividing by a thousand, and that a price per 100 grams multiplied by ten is a price per kilogram. Most shelf-label confusion comes from comparing a per-100g figure with a per-kg one without noticing.

Be careful that the unit is the same on both labels. Stores are allowed to choose a sensible unit for the category, and for things sold in a range of sizes you will sometimes find one label in kr/kg and its neighbour in kr/st.

Where bigger stops being cheaper

The rule of thumb is that the larger pack costs less per unit. It is true often enough that people stop checking, and stores know that. There are three reliable exceptions.

When the small size is on promotion

A discount applies to a specific article, not to the product family. A promoted 500g pack routinely beats the everyday 1kg one, and for the week of the promotion the usual advice is exactly backwards.

When the large size is the premium format

Family packs, resealable tubs and refill cartons are sometimes priced as convenience rather than as volume. This is common in cleaning products and personal care, where the refill is the better deal in some ranges and the worse deal in others.

When you will not finish it

A cheaper kilogram price on something that goes off is not a saving. The relevant figure is the price per unit you actually eat, and for fresh goods in a small household the large pack can lose on that measure by a wide margin even while winning on the label.

Using receipts instead of labels

The shelf tells you today. Your receipts tell you the pattern, and the pattern is more useful.

Once you have a few months of purchases with unit prices attached, you can see which size of a product has been the better value on average rather than on the day you happened to look, whether the gap between sizes is stable or moves with promotions, and which categories are worth checking at the shelf at all.

That last one matters most, because checking everything is not realistic. In most households the money is concentrated in a dozen or so products bought every week. Those are the ones where a six per cent error, repeated fifty times a year, is worth a few seconds of arithmetic. For the long tail of things you buy twice a year, it is not.