Grade 6: Geometry

Find the Volume—with Marshmallows! 

Get a bag of mini marshmallows, liquid glue, and some construction paper. Have your child create rectangular prisms of different sizes with marshmallows, then count the marshmallows to calculate and compare their volumes.  

Begin by asking your child to write the formula for volume on the top of the construction paper. The volume of a rectangular prism is: Volume = length × width × height. 

Then, have your child make their first rectangular prism with the marshmallows. One marshmallow equals one cubic unit. Have them glue each marshmallow onto the paper side by side. The number of marshmallows per column is the length, and the number of marshmallows per row is the width. When your child has determined how long and wide they want the rectangular prism to be, have them glue another layer of the same number of marshmallows on top of the first marshmallows. The number of times the marshmallows are stacked on top of each other is the rectangular prism’s height. 

When your child is done constructing their rectangular prism, have them plug in the prism’s length, width, and height into the formula for volume. To check their work, they can count each marshmallow in the rectangular prism. The numbers should match. 

Calculating volume via a physical activity will help your child better comprehend the concept of volume in the real world. Using concrete objects allows your child to physically manipulate the variables to create rectangular prisms of varying sizes. Your child will be able to compare the rectangular prisms visually and see how changing their lengths, widths, and heights impact their volumes.