Which one’s actually cheaper?

Field notes

What do I put in “quantity”?

The amount in the package, in the same unit for every row: 750 and 1000 (millilitres), 0.75 and 1 (litres), 6 and 10 (eggs) — any consistent choice works, since only the ratio matters.

Why does the shelf label disagree?

Shelf unit prices are sometimes per different base amounts (per 100g vs per kg) or simply missing on promotions — which is precisely when this page earns its keep.

Can I type European decimals?

Yes — 12,5 and 12.5 both work, and thousands separators are fine (1,234.56 or 1.234,56). A lone comma followed by exactly three digits, like 1,234, is read as one thousand two hundred thirty-four.

Where does this run?

Entirely in your browser. Numbers you type are never sent anywhere — there is no server doing the math, no analytics watching you do it.