Unit Price Calculator
Compare two products by price per unit to find the better deal, accounting for pack size and quantity — the bigger package is not always cheaper.
Comment utiliser cette calculatrice
- 1Enter the price and size of the first option.
- 2Enter the price and size of the second option, using the same unit for both.
- 3Read which option is cheaper per unit and by how much.
Comment ça marche
Unit price
unit price = total price ÷ quantity compare the two unit prices directly saving % = (higher − lower) ÷ higher × 100
Unit price strips away package size so two options can be compared fairly: divide each price by its quantity and the lower number wins. It sounds obvious, but retailers exploit the fact that shoppers compare sticker prices rather than unit prices — the larger 'value' pack is often priced to look like a deal while costing more per gram than the small one. A quick unit-price check is the single most reliable way to spot which package is genuinely cheaper.
Exemple détaillé
A 500 g jar at $3.99 works out to $0.798 per 100 g. A 900 g jar at $6.49 is $0.721 per 100 g — so the big jar is about 9.6% cheaper per gram, and the better buy if you will use it all.
Unit Price Calculator : le guide complet
The bigger pack is not always cheaper
There is a widespread assumption that buying in bulk always saves money per unit, and retailers rely on it. Studies of supermarket shelves regularly find larger packages that cost more per unit than the smaller size sitting next to them — sometimes deliberately, because the larger pack looks like a 'value' size and shoppers don't check. The only way to know is to divide price by quantity for each and compare.
This flips the usual advice on its head. Bulk buying pays off only when the unit price is actually lower and you will use the whole amount. A per-unit-cheaper deal on something perishable that you throw half away costs more than the smaller pack you finish. Unit price answers the first question; your own habits answer the second.
Reading shelf labels critically
Many countries require stores to display a unit price on shelf labels precisely so shoppers can compare fairly. But the unit shown is not always consistent — one product may be priced per 100 g and a competing one per kilogram or per item, making direct comparison harder than it should be. Converting to a common unit, as this calculator does, removes the confusion.
Watch for other tricks too. 'Was $5, now $4' framing anchors you to the old price rather than the value; multi-buy offers ('3 for $10') can be worse per unit than the single price; and shrinkflation quietly reduces pack size while holding the price, raising the unit cost without changing the sticker. Unit price cuts through all of these because it only cares about cost per gram.
When the cheapest unit price is the wrong choice
Unit price is a powerful tool but not the only factor. Perishability is the obvious one — the cheapest-per-unit option is no bargain if it expires first. Storage space, the cash tied up in a large purchase, and simple variety all legitimately outweigh a few cents per unit for many households.
There are also cases where a higher unit price genuinely buys more: quality, brand reliability, or ingredients you actually prefer. The point of unit price is not to always buy the cheapest, but to make the trade-off visible. Once you know the big jar is 10% cheaper per gram, you can decide whether that saving is worth it — rather than being misled into thinking the small jar was the better deal when it wasn't.
Questions fréquentes
How do I calculate unit price?
Divide the total price by the quantity. A 500 g item at $3.99 is $3.99 ÷ 500 = $0.00798 per gram, or $0.798 per 100 g. Compare the two unit prices directly — the lower one is the better value for the same product.
Is buying in bulk always cheaper?
No. Larger packages often cost more per unit than smaller ones, despite looking like 'value' sizes. Always check the unit price. And even when bulk is cheaper per unit, it only saves money if you use the whole amount before it spoils.
How do I compare items sold in different units?
Convert both to the same unit before dividing. This calculator does that for you — pick one unit and enter both sizes in it, and it reports each option's price per unit and per 100 units so the comparison is direct.
Why do stores make unit prices hard to compare?
Because shoppers who compare sticker prices rather than unit prices can be steered toward higher-margin packages. Inconsistent units on shelf labels, multi-buy framing, and shrinkflation all obscure the true cost per unit. Calculating it yourself removes the guesswork.