Unit Price Comparator

The 500 g bag at 4.99 or the 2 kg sack at 13.50 — which is actually cheaper? Enter each item's price, quantity and unit, and everything is normalised to a common base (grams, millilitres or pieces) and ranked. The cheapest is starred and every other line shows how much more it costs per unit, as a percentage, so a difference that looks like small change on the shelf becomes a number you can act on.

Mass, volume and count are handled as separate groups because they cannot be compared to each other. A litre of oil and a kilogram of flour are both "one unit" and the comparison means nothing; the tool will not let you mix them, which is a feature rather than a missing one. Within volume, the US units are the US ones: a US fluid ounce is 29.57 ml and an imperial fluid ounce is 28.41, about four percent smaller, so a recipe or a bottle labelled in British fluid ounces is not the same measure. The cup is worse — the US customary cup used here is 236.6 ml while the US legal cup on nutrition labels is 240, a gap of one and a half percent hiding under the same word.

What the arithmetic cannot see is what is in the package. Drained weight and net weight are different numbers on a tin of beans, and comparing the larger figure on one brand against the smaller on another produces a confident wrong answer. Concentrates, dilutable syrups and anything sold by dry weight that you then hydrate all need the comparison done after preparation, not on the label. And the honest limit of unit pricing in general: the cheaper unit price is only cheaper if you use the whole thing. Bulk packs that spoil, go stale or sit unused are more expensive per unit consumed than the small pack you finish, and no calculator can weigh that for you.

Everything runs in the browser, which makes it usable standing in an aisle with no signal. Many countries now require unit prices on shelf labels — the EU and the UK among them — so this is often a cross-check on a number already printed rather than one nobody has computed.