How to Find a Unit Rate (and the Better Buy)

A unit rate tells you how much for exactly one of something: dollars per ounce, miles per hour, words per minute. Dividing by the amount gives you one unit, which makes different deals easy to compare.

Try it with your own problem ↓

The steps

Write the rate as a fraction: the amount you pay (or travel) over the quantity you get.
Divide the top by the bottom to get the amount for 1 unit.
Do the same for the other option, using the same units.
Compare the unit rates. The smaller price per unit is the better buy.

A worked example

Which is the better buy: 12 oz for $3.60, or 16 oz for $4.40?

12 oz for $3.60: 3.60 ÷ 12 = $0.30 per ounce.
16 oz for $4.40: 4.40 ÷ 16 = $0.275 per ounce, which is 27.5 cents.
Compare: $0.275 is less than $0.30.

The 16 oz size is the better buy, at $0.275 per ounce against $0.30. The bigger one is not always cheaper, so always compute it.

Why it works

Packages and trips come in different sizes, so comparing them directly is like comparing apples and oranges. Reducing each one to "per one ounce" puts everything on the same scale. The same idea gives miles per hour, words per minute and cost per item.

Try it with your own problem

Open the free The Ratio Table with this example already filled in. It shows every step, and you can type over it with your own numbers.

Work it out: 12 oz for $3.60 vs 16 oz for $4.40Opens The Ratio Table with this example

Or try these

Common mistakes

Assuming the bigger package is cheaper. Compute both.
Comparing different units. Convert to the same unit (all ounces, all pounds) first.
Dividing the wrong way. Price ÷ amount gives dollars per unit; amount ÷ price gives units per dollar. Use the same one for both products.
Rounding too early. Rounded to the nearest dime, both prices become $0.30 and the better buy disappears.

Questions people ask

What is a unit rate?

A rate with 1 in the denominator, such as 60 miles per hour or $0.30 per ounce.

How do I find speed?

Divide the distance by the time: 150 miles in 2.5 hours is 150 ÷ 2.5 = 60 miles per hour.

What if the sizes use different units?

Convert them first, such as 1 lb = 16 oz, then compare.

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