Course Catalog / BMU 020 / Lesson 1 of 5

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BMU 020

Warm up

1. Think of the last time you stood in front of two sizes of the same thing. How did you pick?

See the answer

Many people pick by the price tag. This lesson shows a better way.

Why this matters

Math at the store is not about tests. It is about getting the most for your money. You are not alone if numbers feel hard. In a 2023 national study, about 34 percent of U.S. adults scored at the lowest level in everyday math.

In this lesson you will use your phone calculator to find the unit price. That is the real cost of each ounce, pound, or count. Then you can see the better buy.

Start with what you already do

You already compare prices. You know a $3 snack costs more than a $2 snack.

Common belief: The big size is always the better deal.

What is actually true: Not always. NIST, the federal office for weights and measures, says the unit price is the best way to compare value. Sometimes the small size costs less per ounce.

Key words

unit price

The cost for one unit, like one ounce, one pound, or one item.

ounce (oz)

A small unit of weight or size. 16 ounces make 1 pound.

better buy

The choice with the lower unit price for the same kind of item.

Your phone calculator

Every smartphone has a calculator app. You need four keys: plus, minus, times, and divide. The divide key looks like this: ÷. The C or AC key clears it so you can start over.

1. Open the calculator app.
2. Type the price.
3. Tap the divide key.
4. Type the size, like the number of ounces.
5. Tap the equals key. The answer is the unit price.

What a unit price is

NIST says a unit price is the cost per unit of measure, like how much you pay per ounce, per liter, or per item. Many stores show it on the shelf tag, often in a small box. Many shopping websites show it too.

NIST reports that in 2024, Purdue University found 82 percent of shoppers use unit pricing when it is shown. If the store does not show it, you can find it yourself.

Find it yourself

Unit price equals price divided by size. Make sure both items use the same unit. Compare ounces to ounces, not ounces to pounds.

The 18 ounce box is the better buy. It costs 5 cents less for each ounce. These prices are made up.

Watch for smaller packages

NIST says some products now come in smaller packages for the same price. This is called shrinkflation. For example, NIST notes a frozen dessert that used to come in 1.5 quarts is now often sold in 1.44 quarts. The unit price shows the change, even when the package looks the same.

Text version of this figure

Find the better buy. Price divided by size.

1. Step 1, Read the price: From the tag or the website.
2. Step 2, Read the size: Ounces, pounds, or count.
3. Step 3, Divide: Price ÷ size on your phone.
4. Same units only: Ounces with ounces, pounds with pounds.
5. Lower unit price wins: That is the better buy.

Source: NIST unit pricing page and SP 1181 (Oct 29, 2026).

Worked example: Lou checks the rice

Lou needs rice. The store has two bags.

• The 2 pound bag is $2.98. He types 2.98 ÷ 2. That is $1.49 per pound.
• The 5 pound bag is $8.25. He types 8.25 ÷ 5. That is $1.65 per pound.
• The small bag costs less per pound this time.
• He buys two small bags and saves 16 cents a pound.

Lou is a made up example. Prices change, so check each time.

Practice: Find the better buy

Divide price by size for each one. The lower unit price is the better buy. All prices are made up.

1. Beans: 15 ounces for $1.20, or 29 ounces for $2.03?
2. Paper towels: 6 rolls for $9.00, or 8 rolls for $11.20?
3. Rice: 2 pounds for $3.00, or 5 pounds for $8.00?

Check your practice: feedback

1. $1.20 divided by 15 is 8 cents an ounce. $2.03 divided by 29 is 7 cents an ounce. The big can is the better buy.
2. $9.00 divided by 6 is $1.50 a roll. $11.20 divided by 8 is $1.40 a roll. The 8 rolls are the better buy.
3. $3.00 divided by 2 is $1.50 a pound. $8.00 divided by 5 is $1.60 a pound. The small bag is the better buy here. Bigger is not always cheaper.

Common mistakes

• Picking the big size without checking. Find the unit price first.
• Comparing ounces to pounds. Change them to the same unit.
• Forgetting to clear the calculator. Tap C or AC before each new problem.

Check your understanding

Take it as many times as you like. Pick an answer, then open the feedback.

1. Pasta is $5.00 for 10 ounces. What does it cost per ounce?

1. 50 cents
2. 2 dollars
3. 5 dollars

See the answer and feedback

A is correct. Yes. 5 divided by 10 is 0.50.

B: You divided the wrong way. Review Find it yourself.

C: That is the whole price. Review Find it yourself.

2. Soap A is $0.12 per ounce. Soap B is $0.09 per ounce. Which costs less per ounce?

1. Soap A
2. Soap B
3. Neither one

See the answer and feedback

B is correct. Yes. 9 cents is less than 12 cents.

A: 12 cents is more. Review the figure.

C: The unit prices are different. Review the figure.

3. Which key do you tap to find a unit price?

1. Times
2. Plus
3. Divide

See the answer and feedback

C is correct. Yes. Price divided by size.

A: Times makes the number bigger. Review Your phone calculator.

B: Plus adds. Review Your phone calculator.

Next up

Next you will use percents for sales, tips, and tax. Go to Lesson 2: Percents, sales, tips, and tax.

Key words: Course glossary (A to Z, with the lesson that teaches each one).

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