What the unit price actually tells you

The unit price in an online shop is the figure shown next to the actual selling price that gives you the price per kilogram, litre, metre or square metre. You usually see it in small print under the big price, something like "3.49 euros (6.98 euros per litre)". The selling price depends on the size of the pack, but the unit price brings everything down to the same unit, so two different-sized packs of the same product can genuinely be compared.

That sounds like a small detail, but it makes a real difference when you shop. Put two bottles of washing-up liquid side by side, one with 500 millilitres for 2.49 euros and the other with 750 millilitres for 3.29 euros, and at first glance it is hard to say which is cheaper. Only the unit price shows which one really costs less.

When a shop has to show the unit price

In the EU, shops have to show a unit price for most pre-packaged goods sold by weight, volume, length or area, such as food, laundry and cleaning products or cosmetics in fixed pack sizes. The rule applies to online shops just as it does to physical stores. Products where a quantity makes little sense are usually exempt, for example items sold individually, like a single tool or a piece of furniture.

These are EU rules that each member state applies through its own national law. Outside the EU, for instance in the UK, the US, Canada or Switzerland, separate rules apply that do not automatically match the EU requirement. If you order from a shop outside the EU, the unit price may be missing or shown differently, and that on its own is not necessarily a sign that the shop is dodgy.

Working out the unit price yourself

If a shop does not show the unit price, or you want to compare two offers that use different units, a simple calculation helps: divide the selling price by the quantity, then scale it up to the unit you want.

Say one shop sells olive oil in a 0.75-litre bottle for 8.25 euros, and another sells the same oil in a 0.5-litre bottle for 5.80 euros. In the first case, 8.25 euros divided by 0.75 gives a price of 11.00 euros per litre. In the second, 5.80 euros divided by 0.5 gives 11.60 euros per litre. Despite the higher overall price, the bigger bottle is the better deal per litre.

Common mistakes when comparing unit prices

• Comparing a price per 100 grams with a price per kilogram without converting one of them first.
• Comparing the unit price of an item on offer with the regular unit price of another product, instead of comparing both under the same conditions.
• Relying only on the first unit price you see when a version in a different pack size only appears after another click.
• Comparing the unit price of a set with that of a single product, even though what is inside is not the same.

Here is an example of the first mistake: one shop lists ground coffee at 1.80 euros per 100 grams, another at 17.50 euros per kilogram. The first figure looks much smaller at first glance. Scale it up to a kilogram, though, and you get 18 euros. So the second offer is 50 cents per kilogram cheaper, even though its number looks ten times bigger.

Most of these mistakes are not down to carelessness. They happen because different shops use different units and different ways of presenting prices. Taking a second look at the unit itself before you put two numbers side by side avoids most of them.

Reading the unit price and discounts together

A discount changes the selling price, but not the size of the pack. When an item is on offer, it is still worth checking the new unit price rather than just the percentage you are saving. In the EU, a price reduction also has to be shown alongside the lowest price of the previous 30 days. That figure tells you whether the current discount really starts from the normal price or only from a price that was raised shortly before the promotion. Shops outside the EU are not necessarily bound by this rule.

When the unit price is missing or unclear

If there is no unit price for a product that ought to have one, there can be several reasons. Some smaller shops keep incomplete product data, while others only show the unit price once you click through to the product details instead of putting it straight into the listing. Before you draw any negative conclusions about the shop, have a look at the product page itself. If the unit price is still unclear there, your own calculation from the selling price and pack size will do the job. How a shrinking pack at an unchanged price affects what you pay is covered in the article Shrinking packs and unit prices when buying groceries.

Using the unit price to compare shops

The unit price is especially useful when you compare the same product across several shops, for example through a category overview. Two shops may stock the same brand in different pack sizes, so comparing selling prices alone can be misleading. The unit price evens that out. How the total cost of an order adds up beyond the item price, for example through delivery charges, is a separate calculation, which the article Working out the total cost of an online purchase walks through.

A valid discount code lowers the selling price or part of the order, but it does not change the unit price of the product itself. A discount on a product with a poor unit price is still a purchase with a poor unit price, just at a lower total. You can find codes for individual shops in the coupon overview on daily-coupons.info.

Frequently asked questions

Does every online shop have to show the unit price?

In the EU, the requirement covers most pre-packaged goods sold by weight, volume, length or area. It usually does not apply to items sold individually or to products without a sensible unit of quantity. Countries outside the EU, such as the UK, the US, Canada or Switzerland, have their own rules.

Why do two shops show different unit prices for the same product?

This mainly happens when the two shops stock different pack sizes of the same product, for example a 500-millilitre and a 750-millilitre version. Each unit price is correct, but it is based on a different starting quantity.

Does the unit price help with sets or bundles?

Only to a limited extent. A set made up of several different products cannot be given a single unit price, because the quantities of the individual parts do not add up to one measure. Here it is more useful to compare the set directly with buying the same items separately.

Does a discount code change the unit price?

No. A discount code lowers the selling price or part of the order, but the pack size, and therefore the underlying unit price, stays the same. A lower final price does not automatically mean a better unit price.