Estimate Lengths in Inches

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Students will estimate lengths using units of inches, feet, centimeter, and meters.

Big Idea

Students will be able to estimate the lengths of objects by mentally partitioning the lengths into inches.

Review It!

20 minutes


 To begin this lesson I invited students to the carpet to watch an  interactive video on how to compare and estimate measurement.  I want students to experience a variety of ways to estimate the length of different objects. Also, Connecting to student’s prior knowledge allows students’  to assess background knowledge before teaching content by linking concepts of measurement to students' personal, cultural, or academic experience.

My goals is to use estimation to develop familiarity with the specific unit of measure being used.

In this lesson we will be focusing on the following Mathematical Practices:  

MP.2. Reason abstractly and quantitatively.

 MP.5. Use appropriate tools strategically.

 MP.6. Attend to precision.




Model and Work Together

20 minutes


The goal of this activity is to have students to look at the length of an object and estimate how long it is before actually measuring it. I ask them to look at their ruler to see how long an inch is before making and estimate. After that, I hold up a pencil. I ask student to guess how many inches it is. Some students guess with out considering the reasonableness of their answers.

I measure the the pencil, and ask students to compare it to what they estimated to see if their given estimation was reasonable. I do this a couple of more times, just to make sure students have a good idea of how estimation works.

I post the following question on the board.


 Marcy moved her desk 7 inches to the right on Monday. She moved her desk 5 more inches to the right on Wednesday.

I ask several volunteers to choose an object in the room that was about 7 or 5 inches. This allows them to keep estimating, even though, I am moving towards a more complex skill. 

Which number line shows how many inches Marcy moved her desk in all? 

(Click here to see the question and answer choices)


Students response:

Together, Jake and Walter jumped 54 inches.


Find the number line that shows a move of 7 to the right. Only X and Z show a move of 7 to the right.

Now, find the number line that shows a move of 5 to the right. Only Z shows this move.

So, the number line labeled Z shows how many inches Marcy moved her desk in all.

Then we discuss how to determine the length of the red line, first figure out the endpoint values. The left endpoint on the red line is 40. The right endpoint on the red line is 50.

Subtract the smaller number from the larger number to find the distance.

50 - 40 = 10

(Review in the same format until a level of understanding is reached before moving to the independent section.) Use the additional practice and explanation sheet to see additional problems. Additional Practice Length Problems.docx

Trying it Out

20 minutes

Students return to their seats to practice on estimating lengths in inches. However, I want  to check for understanding before students began working on the assessment.  I ask students to estimate the total length of the line below.  After they have written their estimation, we discuss how to find the number line that shows a move of 14 to the right.   Then we discuss how to find the number line that shows a move of 3 to the left.  After that, I ask them to explain how to find the total number of moves shown on this number line by writing the number sentence that models the given number line. I ask a few probing question: How do you know? Can you demonstrate? What other unit of measurement can you relate to? 



Student response:


4 + 5 = 9


 After we review estimating lengths and inches.  I give a quick assessment on estimating lengths in inches. I point out that you are to explain or illustrate how many inches were given.  I use data from this assessment to re-teach any misconceptions on estimating lengths in inches.