Converting Weight using U.S. Customary System

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The students will be able to convert measurements of weight within the U.S. Customary System.

Big Idea

Ounces and pounds and tons! Oh, my!


15 minutes

In today’s lesson students explore the weight measurements associated with the U.S. Customary system.  As a class we weigh objects around the room using a bathroom scale and kitchen scale.  Students and I then convert the weights to ounces, pounds, or tons.  Students add to their graphic organizer the weight units and create a tool to convert between the units.  I have the students practice converting using their "conversion tool" and then close the lesson with an exit slip involving some real world problems involving weight conversions.

Students are somewhat familiar with weight measurements so I begin by asking them for some units that would use to measure weight.  I probe student responses until all three weight units are uncovered.  We then add these three units to our graphic organizer for the unit. 

Alright, now that we have the three units we will use for weight conversions what other information do you need in order to convert the measurements?  Talk to your neighbor.

I allow students time to discuss this question with their partner.  The students should be able to discern that they need the conversion factor. 

I think it is important at this point to introduce conversion factor as a part of their math vocabulary.  Additionally, it is easier to use this term instead of saying the number that we use to multiply or divide. 

I explain to students that just like length has conversion factors for the units so does weight. 

Let’s create another conversion tool to use while converting U.S. Customary weight measurements.  What should be in the first box?  Second?  Third?  Now that we have our boxes set up, let’s draw our arrows and add our conversion factors. 

We finish creating the conversion tool and add it to the back of the graphic organizer sheet beneath the length conversion tool. 

To begin the weight measurement investigation I ask for volunteers to be weighed on the bathroom scale.  I record three student’s weights on the board and then proceed to convert these amounts to ounces while students watch and listen.  I ask them to help me first in deciding what operation to use for this type of conversion. 

Are we going from a smaller unit to a bigger unit or a bigger unit to a smaller one?  Okay, so what type of operation are we going to use?  And what will our conversion factor be?

We complete the conversions to ounces for the three students. 


30 minutes

After modeling for the students how to do conversions of pounds to ounces I now have students work in pairs to complete a skills sheet for today.  I allow the students about twenty minutes to complete the conversions while I circulate the room and support students. 

I target students who struggled on their exit slip from yesterday.

At the end of the practice time I call students up to the whiteboard to explain their thinking for solving a specific conversion from the sheet.  I tell students I am not so much interested in the math involved in multiplying or dividing but more interested in how they determined the operation and conversion factor.  While students are presenting their thinking I ensure that students are using the terms converting, conversion factor, and operation.


15 minutes

To wrap up this lesson I have students complete an exit ticket which includes three story problems I created involving converting weight units.  I use this information to guide me in deciding if further clarification is needed in converting weight.  I look to see where students struggled to pin point exactly what part of converting is unclear to them.