Centimeters and Inches

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SWBAT demonstrate an understanding that centimeters are smaller than inches.

Big Idea

How do we understand the difference between inches and centimeters? Why does measuring a given object in centimeters always give a bigger number than measuring the same object in inches?

What is a Centimeter?

10 minutes

I give each child a 6-inch ruler. I ask them how long the ruler is? (6 inches). Is this ruler one foot long? (no) How many of these would you need to make a foot? (2). 

Why are there 2 sets of numbers on these rulers? (inches and centimeters). Does anyone know why we have 2 sets of measurements? (US and most other countries).  What are some things you notice about inches? About centimeters? (I take suggestions here and if appropriate, we check them out using our rulers to see if they make sense, such as inches are bigger.)

Today we are going to try to figure out what happens when we measure in inches and in centimeters. You will have some pages to do that will ask you to measure in both inches and centimeters and some that will ask you to compare 2 figures. 

After we have completed the 2 pages, we will talk about what we notice about measuring in inches and centimeters. You may do a challenge page if you finish before the others. 

Independent Practice

15 minutes

You will start today with 2 measurement pages inch centimeter measures.pdf

The first page asks you to measure the lines in both inches and centimeters and to record both measurements. I tell students that it is going to be important today to be very careful when they measure. If a shape or line is between 2 numbers, they may either record it as the lower number and a half (3 1/2), or they may go to the closest whole number up or down, but they are really trying to be careful to start at the zero point of the ruler and read the number closest to the end of the line or shape (MP6).

The second page tells you whether to measure in inches or centimeters and to tell how much bigger one line is than the other.

I circulate around the room to help students who may be struggling with this activity.

When everyone has completed their work, I ask students to bring their papers to the rug. We look at some of the answers for the first sheet and I create a table of inches and centimeters. What do students notice about the two numbers? (there are always more centimeters than inches, etc.) Why is that? (centimeters are smaller than inches, inches are bigger). I ask students what would happen if I measured them in centimeters and then inches, which number would be bigger? (centimeters) Would that mean that they are taller in centimeters than they are in inches? Why or why not? 

I continue this discussion until I feel that students understand the concept that a centimeter is smaller than an inch, so it will take more centimeters than inches to measure a given object.

Fun with Inches and Centimeters

15 minutes

For this part of the lesson I invite students to return to their desks. I tell them that they will be following directions to make several lines or shapes on their paper. When they are done, they should trace over the shapes and lines in marker so they are visible, and then they can turn them into a picture on their papers. 

I remind them to use pencil first, in case they make a mistake. They will need to draw all the lines and shapes before turning their paper into a creative picture. 

I circulate around to watch as students remember to use centimeters or inches to follow the directions given.