To identify how to work out the area of a square and calculate the area of other common shapes, we first need to address the burning question, what is the area?
The area is the amount of space within the perimeter of a 2D shape. It is measured in square units, such as cm², m², etc.
You can think of the area inside a given shape or space. It refers to how much space is taken up. The larger the shape, the larger the area and perimeter of the shape. Not to be confused with volume, area only refers to space taken up by a flat or 2D object.
As children work with different 2D shapes and work out the area of each, they will discover that different shapes require the use of different formulas and methods to find the area.
Finding the area of different shapes
Now we know what an area is, we can look at different methods to find areas of different shapes. To calculate the area of a shape, you require two measurements, length and width. How you calculate these two measurements and what you do with them to work out the area will vary, depending on the shape.
Children will learn how to calculate the area of different shapes in primary school. They will start by calculating the area of squares and rectangles using the grid method. Then, using this method, they have to count the squares inside a shape to work out the area in cm². Later, they will learn different formulae for working out the area of different shapes.
How to work out the area of a square
When it comes to knowing how to find the area, finding the area of a square is the best place to start. To find the area of a square, we multiply two sides together. As all sides are the same length, it doesn’t matter which two we pick! Let’s take a look at this example together:
- We know that this square’s sides are 8 cm each.
- To find the area, we need to multiply two of them together.
- So, we work out that 8 × 8=64.
- We answer that the area of this square is 64 cm².
Let’s look at how to calculate the area of another square. Soon, your class will have conquered the first step to area mastery.
- This time, our square has sides of 11 cm each.
- To find the area, we need to find the answer to 11 × 11.
- To make this easier, we could work out 11 × 10 and add an extra 11.
- 11 × 10=110, so 110 + 11=121.
- Our final answer is that the area of our square is 121 cm².
How to calculate the area of a rectangle
Now that we know how to find the area of a square, it’s time to move on to the next level of challenge. Working out the area of a rectangle isn’t any more difficult than it is with a square, though we need to be sure that we’re multiplying the length by the width this time. Let’s try this example:
- We’re finding the area of this rectangle, which is 4 m in length and 7 m in width.
- So, to find out the area, we multiply both of them together.
- We need to work out that 4 × 7=28.
- Our final answer is that this rectangle has an area of 28 m².
As you can see, working out the area of a rectangle is as simple as a quick multiplication question. So let’s try one more:
- We will find the area of a rectangle with a length of 9 cm and a width of 6 cm.
- To find the area, we need to find the answer to 9×6.
- We know that 9 × 6=54, so our final answer is that the area is 54 cm².
How to calculate the area of a parallelogram
A parallelogram is like a rectangle that has been pushed to one side. It is a quadrilateral, like a square and a rectangle, because it has four straight sides and four corners. To calculate the area of a parallelogram, you still use the same formula for a square or a rectangle: height × width.
In this example, the area of the parallelogram is 120 cm².
How to find the area of a triangle
Our third challenge is working out how to calculate the area of a triangle. It’s less daunting than it sounds, though, as there’s only one extra step involved. We need to work out half of the total of the base multiplied by the height. In a nutshell, it’s like working out the area of a rectangle, but we halve the multiplication problem before we solve it! Let’s try this example:
- Here, we can see that the triangle’s base is 9 m, and the height is 10 m.
- We need to work out 1/2 × (9 × 10) to get our answer.
- As we know that 9 × 10=90, all we need to do is halve this value.
- 90÷2=45. Our final answer is that the area of this triangle is 45 m².
Your class will soon have mastered three types of areas. Let’s give another example of how to work out the area of a triangle a go before we give them an activity to practice with:
- This time, the base of our triangle is 12 cm, and the height is 8 cm.
- We need to calculate 1/2 × (12 × 8) to find our answer.
- 12 × 8=96, so we must work out half of 96.
- 96÷2=48. Our final answer is that the area of this triangle is 48 cm².
How to calculate the area of a circle
There are a few things we need to know when calculating the area of a circle, and it’s always good to start with the basics. First, a circle is a 2D shape — like any other 2D shape, its area is the amount of space it covers. Bigger circle, bigger area.
Unlike polygons (such as squares, triangles, or parallelograms), we can’t multiply together the length of the sides to find the area. So instead, we use the distance from the edge of the circle to the center.
To find out how to work out the area of a circle, you need to know two words to do with circles:
- Radius: The radius is the distance from the center of a circle to anywhere on its edge.
- Diameter: The diameter is the distance from one side of the circle to the other, through the middle.
The diameter is twice the radius; the radius is half the diameter. Keep reading to find out how to work out the area of a circle using the diameter.
Let’s break that down into a few easy steps:
Step 1: The first step in finding the area of a circle is finding the radius.
Step 2: Once you have the radius, you must square it (multiply it by itself).
Step 3: Now, you must multiply that value by pi. This stage requires using a calculator, as pi is a significant number. However, it can be carried out without a calculator by multiplying your value by 3.14159. Although, this will give you a less accurate answer.
The result of this equation will give you the area of your circle.
The formula is: π × radius × radius or π × radius², simplified to π × r².
How to work out the area of a circle using the radius
- Area of a circle = π × radius × radius
Pi is a Greek letter, spelled pi, and pronounced like pie. Pi is a constant, which means it never changes. It is also irrational, which means it never ends and never repeats. The first 20 digits are:
If you’re using π to find a circle’s area (or circumference), you can use the π button on your calculator or round it to 3.14.
Example 1 — Find the area of a circle using a radius of 5 cm. Give your answer correct to 1 decimal place.
Area = π × radius × radius
We know the radius, so put it into the formula above:
- Area = π × radius × radius
- Area = π × 5 × 5
- Area = 78.5 cm2 (to 1d.p.)
Make sure you give the correct units. Like any other area, the area of a circle is given in square units. That may be cm2, m2, mm2 or km2, among others.
Let’s go through another example.
Example 2 — Find the area of a circle using the radius of 17 cm. Give your answer correct to 1 decimal place.
Area = π × radius × radius
We know the radius, so put it into the formula above:
- Area = π × radius × radius
- Area = π × 17 × 17
- Area = 907.9 cm2 (to 1d.p.)
How to work out the area of a circle using the diameter
In maths, you will not always be given the radius of a circle. However, it is still possible to find the area. Here are the steps you must take to work out the area of a circle using the diameter:
Step 1: Find the radius
The radius is equal to half of the diameter. So, to find the radius, we must divide the diameter by 2:
radius = diameter ÷ 2
Step 2: Use the formula using the radius
Now that we know the radius, we can use the same formula for the area.
Area = π × radius × radius
We are multiplying r by itself in this equation, which means we are squaring it. So, the formula can be simplified into this:
Finally, because this is an algebraic formula, we can remove the × sign:
Let’s put this into practice with an example.
Example 1 — Find the area of a circle using a diameter of 14 m. Give your answer correct to 1 decimal place.
Be careful! We have been given the diameter in this question, but we need the radius to find the area.
The radius is half the diameter:
- radius = diameter ÷ 2
- radius = 14 ÷ 2
- radius = 7 m
We can now find the area as before:
- Area = π × radius × radius
- Area = π × 7 × 7
- Area = 153.9 m2
Here’s another example of how to find the area of a circle using the diameter:
Example 2 — Find the area of a circle using a diameter of 32 m. Give your answer correct to 1 decimal place.
The radius is half the diameter, so:
- radius = diameter ÷ 2
- radius = 32 ÷ 2
- radius = 16 m
Now, we can find the area using the original formula:
- Area = π × radius × radius
- Area = π × 16 × 16
- Area = 804.2 m2
How to work out the area of a circle using the circumference
In some cases, you will find that a circle’s radius and diameter are unknown. Fear not; you can still calculate the area of a circle using the circumference. The circumference is the total distance around the circle. The formula for finding the area of a circle using the circumference is:
C = 2πr
Key:
- C represents the circumference
- r represents the radius
- A represents the area
Step 1: Solve for ‘r’
We can take this formula for the circumference and use it to find the value of the radius. To do this, the formula will be:
r = C/2π
Step 2: Replace ‘r’ in the formula
Now, we can replace ‘r’ in the original formula for the circumference with this new expression:
A = π(C/2π)2
Step 3: Simplify the formula
This formula is quite confusing to look at, so let’s simplify it. The simplified version of this formula for the area of a circle is:
A = C2/4π
Now you have a fool-proof formula for calculating the area of a circle.
Let’s put all of this into practice with an example!
Example 1 — Find the area of a circle using the circumference of 30 m. Give your answer correct to 1 decimal place.
A = C2/4π
Now, we have to put the measurements of the circle into this formula.
A = 302/4π
A = 900/4π
Area = 71.6 m2
How to work out the area of a border
Sometimes, you will encounter a maths problem asking you to find the area of a border, which is a shape within another shape. In this instance, the process for working out the area is slightly different. Let’s work through it with an example:
Work out the area of a rectangular path with a height of 4 meters. The width of this rectangle is 20 meters, and the height is 15 meters.
There are two ways to go about finding the area:
- You could work out the area of this path by splitting it into four rectangles and using the formula discussed above to work out each area. Then, you could add them together to find the total area of the path.
- The other, arguably more efficient, way to work out the area of the path is to calculate the area of the whole shape and the area of the internal shape. Then, subtract the area of the inner shape from the area of the entire shape, and you will be left with the area of the path.
The second method would go as follows:
Step 1: Find the area of the whole shape. Height x width = 15 × 20 = 300 m²
Step 2: Use the path width to work out the area dimensions of the internal shape. If the width of the whole shape is 20 m, and the width of the path is 4 m, we must subtract 4 from 20 on each side.20 – (4 × 2) which becomes20 – 8= 12 metres
So, the width of the internal shape is 12 meters. The same method can be used to find the height of the inner shape.
The height of the whole shape is 15 meters, and the width of the path is 4 meters, so we must subtract 4 from 15 on each side.15 – (4 × 2)whichbecomes15 – 8= 7 metres
The height of the internal shape is 7 meters.
Step 3: Now that we have the dimensions of the internal shape, we can use them to work out the area using our rectangle formula.Height x width=7 × 12= 84 m²
Step 4: Finally, we have both of the measurements we need to work out the area of the path. So, the last step is to subtract the area of the internal shape from that of the whole shape:300 – 84= 216
So, the area of the path is 216 metres²
How to find the area of a shape: irregular shapes
Sometimes, you will come across complicated shapes without a straightforward formula for finding the area in maths. However, if you find yourself in this position, fear not, as there are some simple steps you can carry out to find the area.
Step 1: The first step in finding the area of a complicated shape is to break the figure down into more specific sections. These sections will be smaller shapes within the larger, more complicated one. Looking for right angles and parallel lines is best when finding these smaller shapes.
Step 2: Work out the area of your individual, smaller shapes. This step will look different depending on what forms you are working with. If you need help with this bit, you can look at our sections on how to find the area of a square, circle, etc.
Step 3: Now, you must add the areas of your shapes together, giving you the total area for your irregular shape.