Lesson 8

What is an Inch?

Lesson Purpose

The purpose of this lesson is for students to learn that an inch is a standard length unit in the U.S. customary system and use it to measure length.

Lesson Narrative

In previous lessons, students learned the importance of using standard length units to measure and compare lengths. They learned about length units from the metric system and measured the length of objects in centimeters and meters with different tools, including rulers and meter sticks.

In this lesson, students learn that an inch is a standard unit of measure in the U.S. customary system. They use inch tiles or rulers to measure the length of classroom objects and the sides of geometric shapes in inches (MP2, MP5). Students use their tools and their measurements of classroom objects to develop a benchmark for the length of an inch, which will support them with estimating in later lessons.

Students need access to inch tiles and rulers throughout the lesson, including the cool-down.

  • Representation
  • MLR8

Learning Goals

Teacher Facing

  • Define an inch as a unit of measure.
  • Use a ruler to measure length in inches.

Student Facing

  • Let’s measure in inches.

Required Materials

Required Preparation

Activity 1:

  • Each group of 4 needs access to several objects between 1–11 inches long. Consider using classroom objects such as markers, colored pencils, 11 connecting cubes, books, or any other object with a length shorter than 12 inches.

CCSS Standards


Lesson Timeline

Warm-up 10 min
Activity 1 25 min
Activity 2 10 min
Lesson Synthesis 10 min
Cool-down 5 min

Teacher Reflection Questions

In Activity 2, students estimated the length of objects in inches. Did their previous work measuring and estimating with centimeters make working with a new length unit easier? How have you seen students making progress toward making more accurate estimates?

Suggested Centers

  • Capture Squares (1–3), Stage 4: Subtract within 20 (Supporting)
  • Math Stories (K–2), Stage 5: Tape Diagrams (Supporting)

Print Formatted Materials

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Additional Resources

Google Slides

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PowerPoint Slides

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