When a multibuy isn't the cheapest
A deal makes each pack cheaper, but only if you buy the lot, and the single pack often started dearer per kilo than the big one. Shelf works out the deal price per pack, then the unit price, and tells you how many you need to buy.
Worth it only if you'd use them all before they go off.
Questions
How is the unit price worked out?
Price per pack, after any deal, divided by everything in the pack: size × number in the pack. A 6 × 330 ml pack of cans for 4.50 is 1,980 ml, so 2.27 per litre. Shelf then shows every product in the same unit, even if one tag is in ounces and another in grams.
How do multibuy deals work here?
Pick the deal on the tag. "3 for 6" means each pack costs 2. "Buy 1 get 1 free" halves it. "Second one half price" makes each of the two 75%. Shelf uses that deal price for the comparison and tells you how many you'd have to buy to get it.
Can I compare grams with millilitres?
Not fairly. Weight and volume only match for water, so Shelf compares the products that share a unit type and flags the odd one out. Most tags print both; use the one the others use.
What about toilet paper and kitchen rolls?
Use sheets: rolls go in the pack box and sheets per roll in the size. Big rolls with fewer sheets can still win. If the sheets are a different size, compare by metres instead; most packs print the length.
Does it work offline in the shop?
Yes. After the first visit the page works without signal, and it remembers your last comparison on this phone. Add it to your home screen from the browser's share menu.
Do you keep what I type?
No. Prices stay on this device. We count page views without cookies.