# Volume Rectangular Prisms Lesson 9-9

### Vocabulary

• The

volume

of a three-dimensional figure is the number of cubic units needed to fill the space inside the figure.

• A cubic unit is a cube that measures 1 unit long, 1 unit wide, and 1 unit high.

Counting Cubes • If the figure is split into cubes already, then just count the cubes in one layer and multiply that by the number of layers. The top layer is 4 x 5, or 20 cubic units.

There are 20 cubic units per layer, times 3 layers, for a volume of 60 cubic units.

Using Formulas • To find the volume of a rectangular prism or a cylinder, multiply the

area of the base

by the

height

.

• Volume = Area of Base x height • V = Bh • (The capital B does not stand for base, it stands for

area

of the base.)

### Volume of a Rectangular Prism

V = Bh In this case, the base is a rectangle. The area formula for a rectangle is l x w.

V = (l x w) x h V = (4 x 3) x 12 V = 144 cm 3 Volume gives us cubic units.

### Volume of a Cylinder

5 in 16 in

V = Bh In this case, the base is a circle. The area formula for a circle is  r 2 V = (  r 2 ) x h V = (3.14)(5 2 )(16) V = (3.14)(25)(16) V = 1,256 in 3

Homework Time V = l w h