Area is the amount of space within a shape. To calculate a rectangle's
area, multiply its length by its width. When calculating the area of a
vertical rectangle, such as a window, use height instead of length.
For example, a rectangle is 3 feet long, and 4 feet wide. To calculate
the area, do the following:
length = 3 feet
width = 4 feet
area = 3 feet × 4 feet = 12 square feet
To understand why the length is multiplied by the width, think of a
rectangle as a grid of smaller squares. In the example above, think of
the rectangle as having 3 rows, with each row having 4 squares. The
rectangle would have a total of 12 squares.