Dealophant

The bigger box is not always the better deal, and the shelf is designed so you cannot easily tell. Dealophant is a unit-price search engine: it does the per-ounce, per-count, per-sheet arithmetic across a product’s sizes and multipacks and shows you which one is actually cheaper.

Prices come from Amazon’s own product data rather than a scraper, so what you compare is what is being charged, and a variant that has quietly changed size is caught by the maths instead of slipping past it.

It came out of the CommQuest review work. Testing everyday products means pricing everyday products, and the same spreadsheet kept getting rebuilt by hand until it became a search engine instead.

The categories where it earns its keep are the boring ones bought in bulk: paper goods, cleaning supplies, coffee, pet food, supplements, nappies. These are exactly the products sold in a dozen pack sizes with a dozen different unit prices, and exactly the ones where a household buys the same wrong option every month without noticing.

Search a product and the comparison comes back as cost per unit rather than cost per listing, which reorders the results in a way that is frequently counter-intuitive: the family size loses more often than anyone expects. The site earns affiliate commission when a purchase follows, which is disclosed and does not affect the ordering — the maths decides that, and rigging it would break the only thing the site is for.