Estimating Lengths: How Long Is That?

Math Grades 1st Grade 2:02 Video
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Lesson Description

Learn how to estimate the length of objects using inches and centimeters! We'll practice guessing how long things are by comparing them to known lengths.

Video Resource

Estimating lengths | Measurement and data | Early Math | Khan Academy

Khan Academy

Duration: 2:02
Watch on YouTube

Key Concepts

  • Estimating Length
  • Inches as a Unit of Measurement
  • Centimeters as a Unit of Measurement
  • Comparing Lengths

Learning Objectives

  • Students will be able to estimate the length of an object in inches by comparing it to a reference length.
  • Students will be able to estimate the length of an object in centimeters by comparing it to a reference length.
  • Students will be able to understand that estimation is not an exact measurement but a close guess.

Educator Instructions

  • Introduction (5 mins)
    Begin by asking students what 'estimating' means. Discuss real-life scenarios where we estimate (e.g., how many candies are in a jar, how much time it will take to walk to school). Introduce the concept of estimating length and tell them they will be learning to guess how long things are.
  • Video Viewing (7 mins)
    Play the Khan Academy video 'Estimating lengths'. Pause at key points to ask clarifying questions and ensure understanding.
  • Guided Practice (10 mins)
    Work through estimation problems as a class. Use common classroom objects (pencils, erasers, books). First, show a 1-inch reference (e.g., a line drawn on paper). Ask students to estimate how many inches long each object is. Repeat the process using a 10-centimeter reference.
  • Independent Practice (10 mins)
    Provide students with a worksheet containing pictures of objects and reference lengths (both in inches and centimeters). Students will estimate the length of each object and write their answers on the worksheet.
  • Wrap-up (3 mins)
    Review the key concepts of estimating length and the importance of using a reference. Discuss the difference between estimation and precise measurement.

Interactive Exercises

  • Estimating Scavenger Hunt
    Divide students into small groups. Give each group a list of classroom objects to estimate the length of using inches. Groups must collaborate to make their estimates. The group with the most accurate estimates wins!
  • Length Comparison Game
    Show students two different objects. Ask them which object is longer and by how much (approximately). This reinforces comparing lengths and estimating the difference.

Discussion Questions

  • What does it mean to estimate?
  • Why is it helpful to have a reference length when estimating?
  • How can we use what we already know to help us estimate the size of new things?

Skills Developed

  • Estimation
  • Measurement
  • Comparison
  • Problem-Solving

Multiple Choice Questions

Question 1:

What does it mean to estimate?

Correct Answer: To guess how many.

Question 2:

The line is 1 inch long. About how many inches long is a crayon?

Correct Answer: 4 inches

Question 3:

Which is longer, 1 inch or 1 centimeter?

Correct Answer: 1 inch

Question 4:

If a book is about 10 inches long, is it longer or shorter than 5 inches?

Correct Answer: Longer

Question 5:

If a paperclip is about 3 centimeters long, and a pencil is about 15 centimeters long, which is longer?

Correct Answer: The Pencil

Question 6:

Which of these is the best way to guess how long something is?

Correct Answer: Look at something you know the size of and guess.

Question 7:

Which unit is bigger?

Correct Answer: inch

Question 8:

A desk is about 50 centimeters tall. About how tall is half the desk?

Correct Answer: 25 centimeters

Question 9:

If a pencil is 7 inches long, and a pen is 5 inches long, which is closest to the total length?

Correct Answer: 12 inches

Question 10:

If one sunflower is 40 centimeters tall, and another is half that height, how tall is the second flower?

Correct Answer: 20 centimeters

Fill in the Blank Questions

Question 1:

When we estimate, we make a good ________.

Correct Answer: guess

Question 2:

We can use ______ and _______ to measure how long things are.

Correct Answer: inches and centimeters

Question 3:

A small bug might be 1 _______ long.

Correct Answer: centimeter

Question 4:

A toy car might be 4 ______ long.

Correct Answer: inches

Question 5:

Estimating helps us to _______ about how big or small something is.

Correct Answer: learn

Question 6:

If something is half as long, it means it's divided by ________.

Correct Answer: two

Question 7:

Is something is double the size, it has been multiplied by ________.

Correct Answer: two

Question 8:

The length of your foot is close to 12 ________.

Correct Answer: inches

Question 9:

A pencil is likely closer to 15 ________ long.

Correct Answer: centimeters

Question 10:

Before you measure, always _________.

Correct Answer: estimate

Educational Standards

CCSS.Math.Content.1.MD.A.2:Express the length of an object as a whole number of length units, by laying multiple copies of a shorter object (the length unit) end to end; understand that the length measurement of an object is the number of same-size length units that span it with no gaps or overlaps. Limit to contexts where the object being measured is spanned by a whole number of length units with no gaps or overlaps. CCSS.Math.Content.1.OA.A.1:Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.

Teaching Materials

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