Measuring Lengths in Centimeters and Meters - Third Grade Mathematics

While customary units like inches and feet are common in daily life, the metric system is the universal language of science and international measurement. Built cleanly around powers of ten, the metric system makes measuring length straightforward and intuitive. In this chapter, you will master the two most common metric length units—centimeters and meters—develop estimation benchmarks, and convert between meters and centimeters.

The Two Core Metric Length Units

In third grade, you focus on centimeters and meters:

Unit          Abbreviation    Benchmark Object
Centimeter    cm              The width of a fingernail or button
Meter         m               The width of a standard doorway or the height of a guitar

The relationship between centimeters and meters is built on groups of 100: 1 Meter (m) = 100 Centimeters (cm)

   [---]  <- 1 Centimeter (cm): Small!
             Width of your index fingernail.

   <--------------------------- 1 Meter (m) --------------------------->
   Contains 100 centimeters laid end to end.
   About the distance from the floor to a standard door handle.

Developing Estimation Benchmarks

When deciding whether to measure an object in centimeters or meters, consider its scale:

Use Centimeters (cm) for Shorter Objects:
- Length of an eraser (about 5 cm)
- Length of a new pencil (about 18 cm)
- Width of a textbook (about 20 cm)
- Length of a shoe (about 25 cm)

Use Meters (m) for Longer Distances:
- Length of a school bus (about 10 to 12 m)
- Length of a soccer field (about 100 m)
- Height of a classroom ceiling (about 3 m)
- Width of a classroom chalkboard (about 3 to 4 m)

Converting Between Meters and Centimeters

Because 1 meter equals 100 centimeters, converting from meters to centimeters is as simple as multiplying by 100!

Rule: To convert meters to centimeters, multiply by 100.
      To convert centimeters to meters, divide by 100.

Examples:
1 m = 100 cm
2 m = 200 cm
3 m = 300 cm
5 m = 500 cm
8 m = 800 cm

If a rope is 4 meters long, its length in centimeters is: 4 x 100 = 400 centimeters!

Reading a Metric Ruler

A standard student metric ruler is usually 30 centimeters long.
- Each numbered line represents 1 centimeter.

- Between each centimeter line, there are 10 tiny millimeter marks (each millimeter is 1/10 of a centimeter).

- Always line up the starting edge of your object with the 0 mark on the ruler!


0    1    2    3    4    5    6    7    8    9   10 cm
|----+----+----+----+----+----+----+----+----+----|
[======================]
Crayon ends at 6 cm mark -> Length = 6 cm.

Chapter Practice Exercises

  1. Which unit would you use to measure each item (write "centimeters" or "meters"): a. Length of a playground slide b. Width of a postage stamp c. Height of a sunflower d. Length of a jump rope e. Length of a pair of scissors
  2. Convert between meters and centimeters: a. 2 m = ___ cm b. 6 m = ___ cm c. 400 cm = ___ m d. 900 cm = ___ m e. 7 m = ___ cm
  3. Choose the best estimate: a. A student desk height: 75 cm or 75 m? b. A car's length: 4 cm or 4 m? c. A glue stick length: 8 cm or 8 m?
  4. A runner ran 5 meters. How many centimeters did the runner run?
  5. A wooden plank was 200 centimeters long. A carpenter cut off 65 centimeters. How many centimeters of the plank remain?

Solutions and Step-by-Step Answers

  1. Appropriate units: a. Playground slide -> Meters. b. Postage stamp -> Centimeters. c. Sunflower -> Centimeters or Meters (tall sunflowers). d. Jump rope -> Meters. e. Scissors -> Centimeters.
  2. Conversions: a. 2 m = 200 cm. b. 6 m = 600 cm. c. 400 cm = 4 m. d. 900 cm = 9 m. e. 7 m = 700 cm.
  3. Best estimates: a. Desk height -> 75 cm. b. Car length -> 4 m. c. Glue stick -> 8 cm.
  4. 5 meters x 100 cm per meter = 500 centimeters.
  5. 200 cm - 65 cm = 135 centimeters remaining.