Check Whether the Big Pack Is Actually Cheaper — Free
Bulk buying is sometimes a real 30 per cent saving and sometimes a bigger bag of the same price per kilo with a storage problem attached. Unit price settles it in twenty seconds, and the extra step of applying your own monthly usage turns the shelf comparison into a yearly number.
The proof surface
Free path: the card computes locally in the browser with no key and no account. Where an AI step helps, any free chat assistant works — Google AI Studio's free tier and Groq's free tier were both no-card and rate-limited when this page was reviewed on 2026-09-13 (limits change; check before you rely on them).
Why the flat version breaks
Shelves compare pack prices, and a bigger number looks like a worse deal even when it is not. Dividing by the amount inside is the whole trick — it is the only way to compare a 2 kg bag with three 750 g bags without doing the arithmetic in the aisle.
How to check the packs in four passes
Grams to kilograms, millilitres to litres. One mismatch produces a comparison that is wrong by a factor of a thousand, and it is the most common error in a shop-side calculation.
Prices drift and promotions end. A comparison built from this week's prices with a date on it is worth keeping; one built from remembered prices is worth nothing.
The card states the difference per unit between the best and worst option and then applies it to your usage. That is the number that decides whether the sack is worth the cupboard space.
Storage space, pests, freshness and whether the household will actually finish a 10 kg sack. The cheapest unit price is a fact; whether it is the right purchase is a household decision.
SAMPLE DATA, NOT A VERIFIED CLAIM: Long-grain rice · four packs priced 12 Oct 2026 · best unit price from the 10 kg sack · 1.5 kg used monthly. Replace these values with your own source before you rely on anything.
What breaks first
Comparing pack prices directly
11.49 against 6.20 looks like the sack is worse value, and it is the opposite. Unless the sizes are identical, price alone tells you nothing.
Using optimistic usage figures
Entering consumption you would like rather than consumption you observe makes every bulk purchase look justified. Use the last month's actual, and check it again after a season.
Ignoring the storage cost
A 10 kg sack that goes stale in a damp cupboard is a worse deal than a 2 kg bag. The card prices the goods; the cupboard is your call.
What you pay otherwise
| The usual route | What it leaves out | Cost |
|---|---|---|
| Buying the small pack by default | The unit-price gap, paid every week | a gap that never closes |
| Buying bulk and wasting it | A sack that goes stale before it is finished | the whole pack |
| Shopping at the nearest shop | Convenience pricing on a staple you buy monthly | priced per unit, every month |
| This page + the free shelf-tag gauge | Computed in your tab, result on screen before you type anything | $0 |
Try the free shelf-tag gauge
Four rice packs are already compared by unit price with the gap stated. Change the usage to 4 kg a month and the yearly saving moves.
Open the free shelf-tag gauge →Keep the work if you will use it again
Every option, the unit price, the gap between best and worst, and the saving at your usage, with no account.
Every option, the unit price and the gap stay free. The one-time tier adds the printable shelf-tag card for your wallet plus the saved staples behind it.
Boundary: This compares the prices you enter; it does not account for promotions, storage, spoilage or quality. Check the shelf price and the pack size on the day, and remember that the cheapest unit price is not always the right purchase.