Measuring Length With Metric Units

Lesson Plan - Get It!

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Learn the Metric Units of Length

When talking about length in the metric system, you are answering one question: How long, tall, or far is something?

The metric system uses four main units to measure length, and each one has its own job.

Millimeter (mm)

The millimeter is the tiniest unit of length in this group. It's perfect for measuring very small things.

In fact, one millimeter is about the width of the little metal tip of a pencil. Teeny tiny!

• 1 centimeter = 10 millimeters

• A paperclip is usually about 30 mm long.

• The diameter of a cup might be 85 mm.

Use millimeters for measuring things that are small and detailed, like the thickness of a coin or the width of your fingernail.

Centimeter (cm)

Next up is the centimeter. This one is great for measuring everyday items such as books, pencils, and bananas.

• 1 meter = 100 centimeters

• 1 centimeter = 10 millimeters

• That banana on your kitchen table? It’s probably around 20 cm long.

When something is too big for millimeters but not huge, centimeters are just right.

Meter (m)

The meter is the basic unit of length in the metric system. You’ll use it when measuring people, furniture, or the width of a room.

• 1 meter = 100 centimeters = 1,000 millimeters

• Most adults are less than 2 meters tall.

• A kitchen table might be 1.5 meters long.

• A crosswalk could be about 5 meters wide.

Meters are for things you could walk around or across without getting too tired.

Kilometer (km)

Need to measure something really big? Bring in the kilometer. This is the unit used for roads, distances between towns, or the length of an island.

• 1 kilometer = 1,000 meters

• The distance between two nearby towns could be 5 km.

• A large park might have walking trails that are 2 or 3 km long.

When it would take more than a few minutes to walk it, kilometers are probably what you need.

Summary So Far

• 10 mm = 1 cm

• 100 cm = 1 m

• 1,000 m = 1 km

Each unit is 10 or 100 or 1,000 times bigger or smaller than another, which makes the metric system easy to scale. No weird numbers to memorize—just powers of 10!

Next Up

Now that you’ve learned the four main units of metric length, you’re ready to put that knowledge to work!

Head to the Got It? section to practice picking the right unit for measuring all kinds of real-world objects—tiny, tall, or tremendously long.