Unit Prices: Compare Supermarket Costs with Online Calculators

The unit-price formula is total price divided by total quantity. For solid foods the useful unit is usually 100 g; for liquids it is 100 ml or 1 litre; for countable items it is one unit. The result lets you compare any two packs directly.

Worked example: a 500 g bag of dried pasta is usually priced between €1.50 and €2.00 depending on brand. At €1.50, unit price = €1.50 ÷ 500 g = €0.003 per gram, or €0.30 per 100 g. A 1 kg bag is often €2.50–€3.30; at €2.80, unit price = €2.80 ÷ 1,000 g = €0.28 per 100 g. The larger bag is cheaper per unit, but only by €0.02 per 100 g. If you will not finish it before it goes stale, the smaller bag may be the better buy.

Retailers know shoppers assume bulk is cheaper, so they sometimes price the larger pack at a higher per-unit rate. The only way to be sure is to do the division. In the table below, every larger pack costs more per unit than the smaller one. These are real patterns we have seen on shelves, with prices ranging from about €2.70 to €8.50 depending on brand and promotion. A bigger pack can still make sense if you use it all, but it is never automatically the better deal.

Supermarkets often quote one product per 100 g, the rival per item, and a third per 100 ml or per serving. The purpose is to stop you comparing at a glance. A label that reads €0.62 per item sounds cheaper than €1.80 per 100 g, yet the two may describe an identical product. The fix is to convert both prices to the same unit — per gram, per millilitre or per single item — using the unit-price formula.

Some products cannot be compared by the weight printed on the front. Juice concentrate is sold thick and diluted at home; dried pulses and rice swell when cooked; canned beans, tuna or olives are often labelled with a drained weight that is less than the net weight on the can. Compare the amount you actually eat or drink. Prices for these items range widely, from about €1.20 for a small concentrate to €2.00 for a litre of ready-to-drink juice, so always check the usable quantity.

Three-for-two, buy-one-get-one-half-price and members-only discounts change the unit price, but not always in your favour. A multibuy is only a saving if you needed the extra items, will use them before they spoil, and the discounted unit price beats the normal price of a rival product. Otherwise you have simply spent more in total. A '€3 each or 2 for €5' deal looks like a discount, yet if the single-unit price was inflated to make the deal look better, the real saving may be zero.

A unit-price calculator does the division for you. Ours is one of five calculators we publish on sitea.biz, and they all run entirely in your browser: no data is uploaded, no account is needed, and no lender, retailer or dietitian is involved. We are an independent directory of online calculators, not a financial adviser or healthcare provider, and we also list independent calculator projects on their own subdomains. Enter the total price and the total quantity, choose the unit you care about, and the tool returns the cost per 100 g, per litre, per item or per serving. It is a quick sanity check, not a recommendation to buy.

Unit-price arithmetic is useful, but it is not a substitute for advice. You can run the numbers on one of the online calculators on sitea.biz, yet the result tells you cost per quantity, not whether a product suits your health, your storage space or your overall budget. If you are shopping for a medical diet, managing debt, or buying in bulk for a business, you need a professional — a dietitian, a money adviser or an accountant — not a browser calculator. Nothing in this guide is financial, legal, tax or medical advice.