Unit price calculator

How to work out the unit price

The unit price is the price of the pack divided by how much is in it. A 16 oz box at 2.49 costs 2.49 ÷ 16 = 0.156 per ounce. In metric, a 500 g pack at 1.29 costs 1.29 ÷ 0.5 = 2.58 per kg. Liquids work the same way with fluid ounces or litres, and eggs, rolls or pods with the number of items.

The calculator does this for every offer, marks the lowest unit price in yellow and tells you how much less it costs than the dearest one. There is no currency: use whatever the shelf says.

A worked example

In ounces (US). The calculator opens with three boxes of pasta:

• A: 16 oz at 2.49, or 0.156 per oz
• B: 32 oz at 4.29, or 0.134 per oz
• C: 3 × 16 oz at 6.99, or 6.99 ÷ 48 = 0.146 per oz

B is the better deal, 13.9% less per ounce than A. The three-pack is cheaper per ounce than a single box, but still dearer than the big one.

In grams (UK and elsewhere). A: 500 g at 1.29, 2.58 per kg. B: 1 kg at 2.39, 2.39 per kg. C: 3 × 500 g at 3.49, 3.49 ÷ 1.5 = 2.33 per kg. Here the multipack wins, 9.8% less per kg than A.

Multipacks, fluid ounces and items

For a multipack, enter the size of one item and the number of packs: 3 × 16 oz becomes 16 and 3. The calculator does the multiplication.

With "Volume" the size goes in fluid ounces (US) or millilitres: a gallon is 128 fl oz, a 1.5 L bottle is 1500 ml. With "Count", enter how many items are in one pack, such as a dozen eggs or 4 rolls. If you switch type before typing anything, the calculator loads a matching example: water by volume, eggs by count.

Unit prices on the shelf tag

In the UK, the Price Marking Order 2004 requires shops to show the unit price next to the selling price for most goods sold by weight or volume. In the US there is no federal rule, and only some states require unit pricing, so the shelf tag may be missing or use different units for two brands side by side. The calculator helps in both cases, and with "buy 2, get 1 free" offers that the tag does not always reflect.

Common mistakes

• Comparing pack prices instead of unit prices. The pack that costs least at the till is often the dearest per kg or per ounce.
• Ignoring the drained weight. For canned tuna, beans or pickles, the drained weight on the label is what you eat.
• Mixing ounces and fluid ounces. Ounces measure weight, fluid ounces measure volume. Pick "Weight" or "Volume" to match the label.
• Buying more than you will use. A big pack is only a deal if you finish it before it goes off.