Measurement conversions

Measurement conversions let you change a measurement from one unit to another without changing the actual amount.

Reading is good — doing is better. Practice Measurement conversions as an interactive lesson.

Definition

A measurement conversion is when you rewrite a measurement using a different unit. For example, 12 inches and 1 foot describe the exact same length — you are just switching the label. To convert, you multiply or divide by a special number called a conversion factor that tells you how many of the smaller unit fit into the larger unit.

Remember the rule

Big to small → multiply. Small to big → divide. Always multiply or divide by the conversion factor between the two units.

Key words

Unit: The label on a measurement, like inches, feet, pounds, or liters, that tells you what you are counting.
Conversion factor: The number that connects two units, such as 12 (inches in a foot) or 100 (centimeters in a meter).
Multiply: What you do when you convert from a bigger unit to a smaller unit — you end up with more of the smaller pieces.
Divide: What you do when you convert from a smaller unit to a bigger unit — you group the pieces together.
Customary system: The measurement system used mostly in the United States, using units like inches, feet, miles, ounces, and gallons.
Metric system: The measurement system used in most of the world, based on powers of 10, using units like centimeters, meters, grams, and liters.
Equivalent: Equal in value even though the number or unit looks different — 2 feet and 24 inches are equivalent.
Conversion table: A chart that lists conversion facts you can look up, like 1 yard = 3 feet or 1 kilogram = 1,000 grams.

Worked examples

How many inches are in 4 feet?

→ 4 × 12 = 48 inches · You are going from a bigger unit (feet) to a smaller unit (inches), so multiply by 12.

How many feet are in 60 inches?

→ 60 ÷ 12 = 5 feet · You are going from a smaller unit (inches) to a bigger unit (feet), so divide by 12.

A recipe needs 3 pounds of flour. How many ounces is that?

→ 3 × 16 = 48 ounces · There are 16 ounces in 1 pound, and you are going from bigger to smaller, so multiply.

A fish tank holds 8,000 milliliters of water. How many liters is that?

→ 8,000 ÷ 1,000 = 8 liters · There are 1,000 milliliters in 1 liter. Going small to big means divide.

How many centimeters are in 2.5 meters?

→ 2.5 × 100 = 250 centimeters · There are 100 centimeters in 1 meter. Bigger to smaller means multiply.

A dog weighs 32 ounces. How many pounds is that?

→ 32 ÷ 16 = 2 pounds · Ounces are smaller than pounds, so divide by 16 to get the bigger unit.

Common mistakes

Multiplying when they should divide, or dividing when they should multiply — always ask yourself: am I going to a smaller unit (multiply) or a bigger unit (divide)?
Using the wrong conversion factor, like using 10 instead of 12 for inches-to-feet.
Forgetting that the metric system uses powers of 10 (10, 100, 1,000) while the customary system uses irregular numbers (12, 3, 5,280, 16).
Leaving the answer in the wrong unit — always write the new unit label next to your number.
Trying to convert across systems (like inches to centimeters) without the right cross-system conversion fact.

FAQs

How do I know whether to multiply or divide?

Ask yourself: am I switching to a smaller unit or a bigger unit? If you are going to a smaller unit (like feet to inches), multiply. If you are going to a bigger unit (like inches to feet), divide.

What are the most important conversion facts to memorize?

For customary: 12 inches = 1 foot, 3 feet = 1 yard, 5,280 feet = 1 mile, 16 ounces = 1 pound, 8 fluid ounces = 1 cup, 4 cups = 1 quart, 4 quarts = 1 gallon. For metric: each unit is 10, 100, or 1,000 times the next one.

Why does the metric system seem easier?

Because every conversion in the metric system is a multiple of 10, so you just move the decimal point instead of memorizing strange numbers like 5,280 or 16.

Can I convert between the customary and metric systems?

Yes, but you need a special cross-system fact, like 1 inch = 2.54 centimeters. In 5th grade, your teacher will usually give you those facts if you need them.

What if my answer has a remainder or decimal?

That is normal. For example, 14 inches ÷ 12 = 1 foot with 2 inches left over, which you can write as 1 foot 2 inches or about 1.17 feet.

Do I need to memorize all the conversion facts?

Your teacher may let you use a reference sheet on tests, but knowing the most common ones by heart makes solving problems much faster.

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