Calculators guide
Is the Bigger Pack Cheaper? A Grocery Run in Unit Prices
· 4 min read
The bigger pack is often cheaper per unit, but not always, and the shelf label alone won't tell you. To compare fairly, divide each price by its size after converting every size to the same unit, then pick the lowest result. With a phone and two minutes, you can do that in the aisle for anything sold by weight, volume or count.
Here is one ordinary grocery trip, three decisions, worked through with the Unit Price Calculator. Prices are shown without a currency symbol, so they work in dollars, euros or anything else.
Stop 1: coffee in three different units
The shelf has three bags of the same ground coffee:
- A 340 g bag at 8.99
- A 1 kg bag at 21.50
- An imported 12 oz bag at 7.49
The 12 oz bag looks cheapest at the register, and nobody can compare grams with ounces in their head. Enter each as a product, picking g, kg and oz from the unit menus:
| Product | Price per 100 g | Compared with best |
|---|---|---|
| 1 kg bag | 2.15 | cheapest |
| 12 oz bag | 2.2017 | +2.4 % |
| 340 g bag | 2.6441 | +23 % |
The big bag wins, but only just over the 12 oz bag. The small 340 g bag costs 23 % more per gram. The calculator also reports You save vs. the most expensive: 18.7 %, which is the saving from choosing the 1 kg bag over the 340 g one.
That 2.4 % gap is worth a second thought. If the 1 kg bag would go stale before you finish it, the 12 oz bag costs almost the same per gram and is far less likely to be wasted.
Stop 2: olive oil in liters and fluid ounces
Next, three bottles:
- 500 ml at 6.49
- 1 l at 11.99
- 25.4 fl oz at 9.99
The 25.4 fl oz bottle is about 751 ml, so it sits between the other two in size and looks like a middle-ground deal. The numbers say otherwise:
- 1 l: 1.199 per 100 ml, cheapest
- 500 ml: 1.298 per 100 ml (+8.26 %)
- 25.4 fl oz: 1.3299 per 100 ml (+10.9 %)
The mid-size bottle is the worst value of the three. Odd sizes in less familiar units are a common way for a pack to look like a bargain when it isn't.
Stop 3: paper towels by the roll
For items sold by count, choose item as the unit and enter the number of rolls as the size:
- 6 rolls for 4.99
- 15 rolls for 12.49
- 2 rolls for 2.29
The 6-pack comes out at 0.8317 per item and the 15-pack at 0.8327 per item, just 0.12 % more. The bulk pack gives you no real saving, so buy whichever fits your storage space. The 2-pack, at 1.145 per item, costs 37.7 % more than the best option.
How to run a comparison
- In Product 1 — price, Product 1 — size and Product 1 — unit, enter the first item. The form starts with two sample products filled in, so replace those.
- Repeat for at least one more product, up to four.
- Read the Best value line, then each product's price per unit and how much more it costs than the cheapest. The cheapest is marked "✓ cheapest".
- Open Unit prices in other units to see the same figures per kg, per lb and per oz (or per litre and per fl oz for liquids).
Results update as you type, and the math runs in your browser.
Three things that trip people up
- Mixing weight and volume. You can't compare a 500 g jar with a 1 l bottle without the product's density. If the units come from different groups, the calculator asks you to compare like with like: weight units, volume units or items for all products.
- Half-filled rows. A product counts only when both its price and its size are filled in. If you enter a price but leave the size blank, that product is skipped without a warning, so check that every product you meant to compare appears in the results.
- Size printed in two units. Many packs list both, such as "12 oz (340 g)." Either one gives almost the same unit price (12 oz is 340.2 g), but make sure the size and unit you enter belong together.
When a coupon or sale applies, work out the final shelf price with the Discount Calculator first, then enter that price here.
FAQ
What if two products cost exactly the same per unit?
Both are marked "✓ cheapest", and the savings line is left out because there is nothing to save. At that point, choose on freshness, storage space or brand.
Should I trust the unit price printed on the shelf tag?
It's a useful start, but stores sometimes show different products per 100 g, per kg or per item, even in the same aisle. Entering the sizes yourself puts every product on the same basis.
Does it work for things like data plans or detergent loads?
Yes, if you treat them as a count. Enter loads or gigabytes as items and the result is a price per load or per gigabyte.
Make your next shelf decision in seconds with the Unit Price Calculator.