Unit pricing explained: how to compare price per kilo, per litre and per item
Quick answer: A unit price is the price for a standard quantity, such as one kilogram, one litre or one item, and it lets you compare packs of different sizes fairly. To work it out, divide the price by the quantity. In Great Britain the Price Marking Order 2004 requires many shops to display it, and since 6 April 2026 unit prices are shown per kilogram, litre or metre, or per item for goods sold by number.
Last updated: 12 November 2026
Pack sizes are rarely designed to make comparison easy: 500 ml next to 1.35 litres, four tins next to six, 40 washes next to 50. The unit price cuts through that. It answers one question: how much am I paying for the same amount of product?
Selling price and unit price
The Price Marking Order 2004 uses two terms. The selling price is the final price for one unit or a given quantity of a product, including VAT and all other taxes. The unit price is the final price, on the same basis, for a standard measure: one kilogram, one litre, one metre, one square metre or one cubic metre, or a single item for goods sold by number.
When shops have to show it
- Which products. Government guidance explains that a unit price is required for products sold loose from bulk, and for products that weights and measures law requires to be marked with a quantity or made up in a prescribed quantity. That covers most packaged food, drink and many household products.
- Small shops. Shops with a floor area of 280 square metres or less don't have to show unit prices on pre-packaged products in constant quantities, although they must still do so for goods sold loose.
- Online. The Order covers online sales of goods as well as physical shops. An advertisement doesn't have to show a price, but if it does, it must show the unit price where one is required.
- When it isn't needed. No separate unit price is needed where it would be identical to the selling price, for example a 1 kg bag.
- Precision. Unit prices below £1 are shown to the nearest 0.1p.
- Where. The Order applies in England, Scotland and Wales. Northern Ireland has its own, similar Price Marking Order.
What changed in April 2026
Amendments to the Order took effect on 6 April 2026. Before then, a schedule to the Order set different units for particular products, which is why some shelf labels showed a price per 100 g or per 100 ml. That schedule has been removed. Trading Standards' Business Companion summarises the position: all unit pricing is now the price per kilogram, litre, metre, square metre or cubic metre, as appropriate. The amended Order also requires prices to be shown in a clear font of a reasonable size, requires each selling price and unit price to be shown where a product has more than one price (such as a loyalty-scheme price), and treats any deposit separately from the price.
How to work it out yourself
Unit price = price ÷ quantity. Put the quantity into kilograms or litres first (500 ml is 0.5 litres; 400 g is 0.4 kg). All the prices below are invented examples for illustration.
| Example | Pack A | Pack B | Better value |
|---|---|---|---|
| Washing-up liquid | 500 ml at £1.50 = £3.00 per litre | 1.35 litres at £3.65 = £2.70 per litre | Pack B |
| Tinned tomatoes | Single 400 g tin at 95p = £2.38 per kg | Four 400 g tins at £3.40 = £2.13 per kg | Pack B |
| Toilet roll, per roll | 9 rolls at £4.95 = 55p per roll | 24 rolls at £11.52 = 48p per roll | Pack B, on this measure |
| The same toilet roll, per 100 sheets | 9 rolls of 220 sheets = 25p per 100 sheets | 24 rolls of 160 sheets = 30p per 100 sheets | Pack A |
| Laundry liquid, per wash | 1.2 litres, 40 washes, at £6.00 = 15p per wash | 2 litres, 50 washes, at £8.50 = 17p per wash | Pack A, although B costs less per litre |
Example prices only. The toilet roll and laundry rows show why the unit on the label is not always the unit that matters.
Multibuys and bigger packs
A multibuy is a unit-price question in disguise. If one bottle costs £1.80 and the offer is "3 for £5", each bottle in the offer costs £1.67, but only if you buy three and use all of them. A bigger pack is not always better value either: compare the unit price, then ask whether you will finish it before it goes off or runs out of date.
Five things that catch people out
- Different measures for similar products. One product priced per kilogram and its neighbour priced per item can't be compared directly. Convert one of them.
- Concentrates. For laundry liquid, dishwasher tablets or squash, the cost per wash or per serving matters more than the cost per litre.
- Sheets, not rolls. For kitchen roll and toilet tissue, the number of sheets per roll varies widely.
- Shrinking packs. If a pack gets smaller while the price stays the same, the selling price doesn't change but the unit price does. Checking the unit price is how you notice.
- Quality. The unit price compares quantity, not quality. It is one input to the decision, not the whole decision.
Unit pricing when you shop online
Online grocers usually show the unit price beside or beneath the selling price. Where a listing doesn't show one, the calculation takes seconds: find the net quantity in the product details and divide. Our Measurement conversion charts help when quantities are given in ounces, pounds or US fluid ounces.
At Bargain Catcher the comparison is simpler because delivery is free on every order, so there is no delivery charge to factor in. Our How we price page explains how we show prices. Products where pack-size comparisons come up most are in Health & Household, Home & Kitchen, Pet Supplies and Baby & Nursery.
Related: How to tell if a discount is real · Your rights when you shop online in the UK · UK sales calendar · FAQ.
This guide is general information, not legal advice. It describes the position for consumers in the UK on the date shown above; for advice about your own situation, contact Citizens Advice or a qualified adviser.