Use the free Unit Price Comparison Calculator below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
The Pack Price Lie
Supermarkets know that shoppers compare pack prices, so they make pack prices hard to compare. One pack costs 4 for 10 units, another costs 7 for 20 units, a third costs 5.50 for 15 units, and the cheapest pack is not the cheapest product. This calculator cuts through that confusion by dividing price by quantity for each pack, ranking the packs by price per unit, and showing how much more each pack costs than the cheapest one. The answer is often surprising, and the savings add up fast on goods you buy every week.
The trick works because our brains compare the big number first. A 4 pack feels cheaper than a 7 pack, even when the 7 pack contains twice as much and costs less per unit. Stores exploit that instinct with pack sizes that change slightly, with multibuys that look like deals, and with premium packaging that hides a higher unit price. Dividing price by quantity is a small habit that defeats all of those tricks at once.
How the Calculator Works
That percentage is the most useful number for quick decisions. A pack that costs 20 percent more per unit may still be worth buying if it is the only size you can carry, store, or use before it spoils. A pack that costs 60 percent more per unit is rarely worth it unless the cheaper pack is enormous, perishable, or sold out. Use the percentage to judge, not just the ranking, because a tiny percentage gap may not justify changing brands.
A Worked Example
Now add a trap. Pack D costs 3 for 500 grams, which looks like the cheapest pack of all, but its unit price is 6 per kilogram, making it 71 percent dearer than Pack B. Small packs almost always carry the highest unit price, because packaging and handling cost nearly as much for a small pack as for a large one. If you have storage space and the product keeps well, larger packs usually win, but only the division proves it for each product.
When the Cheapest Per Unit Is Not the Best Buy
Unit price is a powerful guide, but it is not the whole story. Perishable food can spoil before you finish a large pack, turning a cheap unit price into wasted money. A bulk pack you cannot store properly can go stale, leak, or attract pests. A product you dislike in bulk is a worse deal than a smaller pack you actually enjoy, because the saving is meaningless if half the pack ends up in the bin.
Cash flow matters too. A bulk pack that saves 20 percent but costs 40 upfront may strain a tight weekly budget, even though it saves money over the month. In that case, buy the smaller pack this week and plan the bulk purchase for a week when cash is easier. Saving money should never mean going short on rent or bills to stockpile rice.
Shopping Habits That Save Real Money
Check the shelf-edge unit price when stores show it, but verify it yourself for important purchases, because shelf labels can use different units for different brands. One brand may show price per 100 grams while another shows price per kilogram, which makes comparison harder than it should be. The calculator removes that problem by forcing every pack into the same division.
Keep a short list of your most-bought goods and their best unit prices. Coffee, rice, pasta, cleaning products, nappies, and pet food are usually the biggest wins, because you buy them often and the pack sizes vary wildly. Once you know the best unit price for each, you can spot a real deal instantly and ignore fake discounts that still leave the unit price above your known best.
Frequently Asked Questions
What quantity should I enter? Whatever unit is printed on the pack and shared across packs: weight, volume, count, or sheets. Never mix units, because grams divided into a litre price gives a meaningless number.
Do multibuys count as one pack? Treat a multibuy as one combined pack: add the prices together and add the quantities together, then enter the totals. That gives the true unit price of the deal.
Is a bigger pack always cheaper per unit? Usually, but not always. Promotions, clearance stock, and own-brand pricing can make a smaller pack cheaper per unit, which is exactly why checking beats assuming.
Use the tool above before your next shop, and let price per unit, not pack price, decide what goes in the basket.
Disclaimer: The results shown by this tool are ESTIMATES only. They are for education and planning, not financial or tax advice. Your real amounts will differ because rates, taxes, fees and prices change. Talk to a qualified financial or tax professional before you make a money decision.