Quick answer

To find out which product gives you the best price, use this formula:

Product price ÷ total quantity = unit price

Then compare the results. The product with the lowest unit price gives you more for your money, even if it has the highest shelf price.

Concept used: unit pricing

This calculator applies the concept of unit pricing. The total price of each product is divided by a common measure — such as meter, kilogram, liter, gram, or unit — to allow a direct comparison between packages of different sizes. This makes it possible to find out which option gives you more product for the money you pay.

Example 1: how to compare toilet paper prices

Imagine two packs of toilet paper, both with 8 rolls:

  • Pack A: costs $51.00 and has 30 meters per roll.
  • Pack B: costs $80.00 and has 55 meters per roll.

Which pack of toilet paper is cheaper?

First, we calculate the total length of each pack:

  • Pack A: 8 rolls × 30 meters = 240 meters
  • Pack B: 8 rolls × 55 meters = 440 meters

Then, we divide the price by the total length:

  • Pack A: $51.00 ÷ 240 = $0.2125 per meter
  • Pack B: $80.00 ÷ 440 = $0.1818 per meter

(The prices used in these examples are illustrative)

Rounding the values:

  • Pack A: about $0.21 per meter
  • Pack B: about $0.18 per meter

Comparison result

Pack B is cheaper per meter, even though it costs $80.00 on the shelf. It saves you about 14% more per meter than pack A.

So when both options fit your budget, it is not enough to compare the package prices. You also need to check how many meters of paper each pack gives you.

Formula for comparing toilet paper

Pack price ÷ total number of meters = price per meter

Example 2: how to compare products with different weights

Imagine two bags of rice:

  • Bag A: holds 800 g and costs $7.20
  • Bag B: holds 1 kg and costs $8.50

Bag A costs less on the shelf. But that does not mean it has the lowest price per kilo.

Which bag of rice is cheaper?

Since 1 kg equals 1,000 g, we first calculate the price per gram:

  • Bag A: $7.20 ÷ 800 g = $0.009 per gram
  • Bag B: $8.50 ÷ 1,000 g = $0.0085 per gram

We can also convert the results to a price per kilo:

  • Bag A: $9.00 per kilo
  • Bag B: $8.50 per kilo

Comparison result

Bag B is cheaper per kilo, even though it has the higher shelf price.

By choosing bag B, the shopper saves:

$9.00 − $8.50 = $0.50 per kilo

That is a saving of about 5.6% per kilo.

How much can a family save with this comparison?

Consider a person who eats 100 g of cooked rice per meal, five times a week.

Since 100 g of cooked rice comes from roughly 33 g of uncooked rice:

  • Weekly consumption: 33 g × 5 meals = 165 g of uncooked rice
  • Yearly consumption: 165 g × 52 weeks = 8.58 kg of uncooked rice
  • How long a 1 kg bag lasts: about 6 weeks

Now consider a family of four with the same consumption:

  • Cooked rice per meal: 100 g × 4 people = 400 g
  • Uncooked rice per meal: about 132 g
  • Weekly consumption: 132 g × 5 meals = 660 g
  • Yearly consumption: 660 g × 52 weeks = 34.32 kg

At this rate, a 1 kg bag would last about 10 or 11 days. The family would go through a little over 34 kg of rice per year.

Since bag B saves $0.50 per kilo:

34.32 kg × $0.50 = $17.16 saved per year

The figures for cooked rice are estimates, since the yield can vary depending on the type of rice and the amount of water used when cooking.

$17.16 may not sound like much. But this saving comes without changing any habits: you just make the comparison once and pick the bag with the lowest price per kilo on your next shopping trips.

Now imagine applying the same calculation to many products you buy during the year. Comparing the unit price helps you save without eating less or going without what your family needs.

Formula for comparing products by weight

Product price ÷ total weight = price per gram

To find the price per kilo:

Product price ÷ weight in grams × 1,000 = price per kilo

Frequently asked questions

Is the product with the lowest price tag always the cheapest?

No. A package may cost less because it contains a smaller amount. To compare correctly, check the price per gram, kilo, liter, meter or item.

What is unit price?

Unit price is the amount you pay for one specific measure of the product. It can be the price per gram, kilo, liter, meter, sheet, pod or item.

How do you calculate the price per unit?

Divide the product's total price by the quantity it contains:

Price ÷ quantity = unit price

How do you compare packages of different sizes?

Convert both packages to the same unit of measure. For example, turn 1 kg into 1,000 g before comparing a 1 kg bag with an 800 g one.

Is it worth buying the bigger package?

Not always. The bigger package only gives you a financial advantage when its unit price is lower and you can use the product before it expires or goes bad.

Which product should I choose?

When both options fit your budget and are of similar quality, choose the one with the lowest unit price.

Warning: the lowest price per unit does not take quality, expiration date or waste into account.