Measuring in Centimeters and Meters - Second Grade Mathematics

While the United States frequently uses customary inches and feet, scientists, doctors, engineers, and citizens in almost every country around the globe use the metric system. The metric system is a clean, base-ten measurement system where all units connect by powers of 10, making it one of the most elegant scientific inventions in human history. The two most common metric units of length in second grade are the centimeter and the meter. In this chapter, you will master measuring with a centimeter ruler, understand the 100-to-1 relationship between centimeters and meters, and compare metric units directly with customary units.

The Centimeter: Small and Precise

A centimeter (abbreviated cm) is a metric unit of length that is significantly smaller than an inch.

The Centimeter Scale on a Ruler:
|---|---|---|---|---|---|---|---|---|---|
0   1   2   3   4   5   6   7   8   9   10  (centimeters)

Visualizing a Centimeter

Look at your little finger: the width of your pinky finger across the fingernail is approximately 1 centimeter! Other 1-centimeter benchmarks: The width of a standard staple. The thickness of a wooden pencil. The width of a single base-ten unit cube (exactly 1 cm x 1 cm x 1 cm!). Because centimeters are smaller than inches, they provide greater precision when measuring small items.

Comparing Centimeters to Inches

One inch is equal to approximately 2 and a half centimeters (1 inch = 2.54 cm). That means an inch is much longer than a centimeter! If you place a 1-inch block next to a 1-centimeter block, the inch block is more than double the length of the centimeter block.

The Meter: The Great Base-Ten Benchmark

The foundation of metric length is the meter (abbreviated m).

The Grand Metric Relationship:
100 Centimeters (cm)  <====== EQUAL TO ======>  1 Meter (m)

+--------------------------------------------------------------------------+
|                        1 METER (100 CENTIMETERS)                         |
+--------------------------------------------------------------------------+

The Base-Ten Beauty of the Metric System

Notice how the metric system mirrors our base-ten number system: Just as 100 ones make 1 hundred in place value, exactly 100 centimeters combine to create 1 meter! The word centi- comes from the Latin word for one hundred (just like 100 cents make 1 dollar, or 100 years make 1 century).

Real-World Benchmarks for 1 Meter

One Meter: The width of a standard classroom doorway. The height from the floor to the doorknob. The width of an adult's outstretched arm span from the center of the chest to the fingertips.

Measuring to the Nearest Centimeter

Measuring with a centimeter ruler follows the exact same zero-alignment rule as customary measurement.

Measuring a Crayon to Nearest Centimeter:
Crayon: [====================================]
Ruler:  |---|---|---|---|---|---|---|---|---|
        0   1   2   3   4   5   6   7   8   9 (cm)
Result: Exactly 8 centimeters long!

Nearest Centimeter Rounding

Look at the tip of the object: Each centimeter on a ruler is divided in half by a medium tick mark (representing 5 millimeters, or half a centimeter). If the object ends before the halfway mark, round down to the lower centimeter. If the object ends at or past the halfway mark, round up to the higher centimeter.

Practice Exercises

Exercise 1: What is the abbreviation for centimeter, and what is the abbreviation for meter?

Exercise 2: How many centimeters are in 1 whole meter? How many centimeters are in 3 meters?

Exercise 3: Name two everyday physical objects or body parts that can be used as rough mental benchmarks for 1 centimeter and 1 meter.

Exercise 4: A student measures a marker using both an inch ruler and a centimeter ruler. The student gets measurements of 12 and 5, but forgets which number goes with which unit. Match the numbers 12 and 5 to centimeters and inches, and explain your reasoning.

Solutions and Explanations

Solution to Exercise 1: The abbreviation for centimeter is cm. The abbreviation for meter is m.

Solution to Exercise 2: There are exactly 100 centimeters in 1 meter. For 3 meters, multiply or add: 100 + 100 + 100 = 300 centimeters.

Solution to Exercise 3: A good benchmark for 1 centimeter is the width of a child's pinky finger (or the width of a base-ten unit cube). A good benchmark for 1 meter is the width of a standard classroom doorway (or the height from the floor up to a doorknob).

Solution to Exercise 4: The measurement is 12 centimeters and 5 inches. Because a centimeter is significantly smaller than an inch, it takes many more centimeters to span the exact same length than inches. Therefore, the larger number (12) belongs to the smaller unit (centimeters), and the smaller number (5) belongs to the larger unit (inches).