Area is the measure of the amount of surface covered by something. Area formulas
shapes are sometimes different, but for the most part, area is calculated
by multiplying length times width. This is used when calculating area of squares
and rectangles. Once you have the number answer to the problem, you need to figure
out the units. When calculating area, you will take the units given in the problem
(feet, yards, etc) and square them, so your unit measure would be in square feet
(ft.2) (or whatever measure they gave you).
Area Example 1
Let’s try an example. Nancy has a vegetable garden that is 6 feet long and 4 feet
wide. It looks like this:
Nancy wants to cover the ground with fresh dirt. How many square feet of dirt would
We know that an answer in square feet would require us to calculate the area. In
order to calculate the area of a rectangle, we multiply the length times the width.
So, we have 6 x 4, which is 24. Therefore, the area (and amount of dirt Nancy would
need) is 24 square feet.
Area Example 2
Let’s try that one more time. Zachary has a wall that he would like to paint. The
wall is 10 feet wide and 16 feet long. It looks like this:
to find area of this rectangle, we would multiply the length times the width. When
you multiply 10 x 16, you get 160. Therefore, your answer would be that Zachary
will be painting 160 square feet of wall.
Using Area and Perimeter Together
Sometimes, you will be given either the area or the perimeter in a problem and you
will be asked to calculate the value you are not given. For example, you may be
given the perimeter and be asked to calculate area; or, you may be given the area
and be asked to calculate the perimeter. Let’s go through a few examples of what
this would look like:
Area and Perimeter Example 1
Valery has a large, square room that she wants to have carpeted. She knows that
the perimeter of the room is 100 feet, but the carpet company wants to know the
area. She knows that she can use the perimeter to calculate the area.
What is the area of her room?
We know that all four sides of a square are equal. Therefore, in order to find the
length of each side, we would divide the perimeter by 4. We would do this because
we know a square has four sides, and they are each the same length and we want the
division to be equal. So, we do our division—100 divided by 4—and get 25 as our
answer. 25 is the length of each side of the room. Now, we just have to figure out
the area. We know that the area of a square is length times width, and since all
sides of a square are the same, we would multiply 25 x 25, which is 625. Thus, she
would be carpeting 625 square feet.
Area and Perimeter Example 2
Now let’s see how we would work with area to figure out perimeter. Let’s say that
John has a square sandbox with an area of 100 square feet. He wants to put a short
fence around his sandbox, but in order to figure out how much fence material he
should buy, he needs to know the perimeter. He knows that he can figure out the
perimeter by using the area.
What is the perimeter of his sandbox?
We know that the area of a square is length times width. In the case of squares,
these two numbers are the same. Therefore, we need to think, what number times itself
gives us 100? We know that 10 x 10 = 100, so we know that 10 is the length of one
side of the sandbox. Now, we just need to find the perimeter. We know that perimeter
is calculated by adding together the lengths of all the sides. Therefore, we have
10 + 10 + 10 + 10 = 40 (or, 10 x 4 = 40), so we know that our perimeter is 40 ft.
John would need to buy 40 feet of fencing material to make it all the way around
Calculating Area and Perimeter Using Algebraic Equations
So far, we have been calculating area and perimeter after having been given the
length and the width of a square or rectangle. Sometimes, however, you will be given
the total perimeter, and a ratio of one side to the other, and be expected to set
up an algebraic equation (using variables) in order to solve the problem. We’ll
show you how to set this up so that you can be successful in solving these types
Eleanor has a room that is not square. The length of the room is five feet more
than the width of the room. The total perimeter of the room is 50 ft. Eleanor wants
to tile the floor of the room. How many square feet (ft 2) will she be
In this problem, we will be calculating area, but first we’re going to use the perimeter
to figure out the length and width of the room.
First, we have to assign variables to each side of the rectangle. X is the most
often used variable, but you can pick any letter of the alphabet that you’d like
to use. For now, we’ll just keep things simple and use x. To assign a variable to
a side, you first need to figure out which side they give you the least information
about. In this problem, it says the length is five feet longer than the width. That
means that you have no information about the width, but you do have information
about the length based on the width. Therefore, you’re going to call the width (the
side with the least information) x. Now, the width = x, and x simply stands for
a number you don’t know yet. Now, you can assign a variable to the length. We can’t
call the length x, because we already named the width x, and we know that these
two measurements are not equal. However, the problem said that the length is five
feet longer than the width. Therefore, whatever the width (x) is, we need to add
5 to get the length. So, we’re going to call the length x + 5.
Now that we’ve named each side, we can say that width = x, and length = x + 5. Here’s
a picture of what this would look like:
Next, we need to set up an equation using these variables and the perimeter in order
to figure out the length of each side. Remember, when calculating perimeter you
add all four sides together. Our equation is going to look the same way, just with
x’s instead of numbers. So, our equation looks like this:
x + x + x + 5 + x + 5 = 50
Now, we need to make this look more like an equation we can solve. Our first step
is to combine like terms, which simply means to add all the x’s together, and then
add the whole numbers together (for more help on this, see Combining
Once we combine like terms, our equation looks like this:
4x + 10 = 50
Next, we follow the steps for solving equations. (For additional help with this,
Solving Equations). We subtract 10 from each side of the equation, which
leaves us with the following:
4x = 40
Now, we have to get x by itself, which means getting rid of the 4. In order to do
this, we need to perform the opposite operation of what’s in the equation. So, since
4x means multiplication, we need to divide by 4 to get x alone. But remember, what
we do to one side, we have to do to the other side. After dividing each side by
4, we get:
x = 10
Next, we have to interpret what this means. We look back and recall that we named
the width x, so the width is 10. Now, we need to figure out the length. We named
the length x + 5, so that means we have to substitute 10 in for x, and complete
the addition. Therefore, we have 10 + 5, which gives us 15. So, our length is 15.
Now, we need to look back and remember that the problem asked us to calculate the
area of the floor that Eleanor will be tiling. We know that in order to calculate
area, we need to multiply the length times the width. We now have both the length
and the width, so we simply set up a multiplication problem, like this: 10 x 15
= ? We multiply the two numbers together, and get 150.
Thus, your final answer is 150 ft 2.
Area and Perimeter Practice Problems
Now, we’ll give you several practice problems so that you can try calculating area
and perimeter on your own.
1. Leah has a flower garden that is 4 meters long and 2 meters wide. Leah would
like to put bricks around the garden, but she needs to know the perimeter of the
garden before she buys the bricks.
garden is 4 meters long and 2 meters wide. Therefore, we would add together 4 +
4 + 2 + 2 = 12 meters. So, the perimeter of the garden is 12 meters.
2. David has a rug that is square, and the length of one side is 5 feet. He has
an open floor space in his living room that is 36 square feet.
Choices: fit perfectly, too big, too small)
told us this). The area of the rug is only 25 square feet (we got this by multiplying
5 x 5 = 25). So, he could put the rug there, but it would be too small (it would
not cover the entire area).
3. Debbie has pool in her back yard that has a perimeter of 64 feet. The length
of the pool is 2 feet longer than the width. Debbie wants to buy a cover for the
pool, and needs to know how many square feet she needs to cover.
set up an algebraic equation to solve this problem!)
and the length x + 2, because the problem says that the length is 2 longer than
the width. We know that to figure out perimeter, we need to add together all four
sides. Thus, our equation would look like this: x + x + x + 2 + x + 2 = 64. This
is shown in the diagram below:
When we combine like terms, we would get 4x + 4 = 64. Then, we would continue solving
normally by subtracting 4 from each side, so the equation would simplify to 4x =
60. Lastly, we would divide each side by 4 (to get x by itself) and we would reach
the conclusion x = 15. Thus, the width of the pool is 15 ft. However, the length
is 2 more than the width, which means we would have to add 2 to the width; 2 + 15
= 17. Now, we have the length (17) and the width (15). The question asked for the
area (square feet) of Debbie’s pool. To find area, you need to multiply the length
times the width. Therefore, you would multiply 17 x 15, which gives us 255. Thus,
Debbie would need a cover for her pool that is 255 feet2.
4. Hector is planting a square garden in front of his house. He wants to plant carrots
in the garden. He knows he can plant the carrots one foot apart. He has six feet
across his yard (length) and he can plant carrots four feet deep (width).
would multiply 4 x 6 and get 24 square feet as the amount of space that he can plant
5. Amanda is building a house, and she’s trying to calculate the area of her bedroom.
She knows that the living room is 22 feet long and 20 feet wide. She was told that
her bedroom should be half of the area of the living room.
the living room. Thus, we first have to figure out the area of the living room.
The dimensions of the living room are 22 feet by 20 feet, so we have to multiply
these two numbers together to get the area. 22 x 20 = 440 square feet. Next, we
have to divide that number by 2, because her bedroom is only half the area of that
room. So, 440 divided by 2 equals 220. Therefore, the area of Amanda’s room would
be 220 ft2.