# Python program to find area of circle

In this post, you will learn about different **Python programs** to find **the area of the circle**. As we all know, the area of the circle is the measure of the space or region enclosed inside the circle. In geometry, the area enclosed by a circle of radius **r** is **πr ^{2}**. Here is the simple formula for calculating the area of the circle.

**Area = pi * r2**

## Algorithm

```
1. Define a function to calculate area
2. Set PI as constant and initialize to 3.147
3. Use the formula of the Area =
```**πr²**.
3. Take input of radius from the user
4. Pass radius in the function
5. Print the result

## Python program to find area of circle using radius

If we know the radius of a circle, then we can easily calculate the area using the formula: **A=πr²**. Here is the simple Python program to calculate the area of a circle using the radius.

```
# program to calculate
# area of circle
def area_of_circle(r):
PI = 3.142
return PI * (r*r);
# get user input
radius = float(input("Enter the radius: "))
# print area of circle
print("Area is %.6f" % area_of_circle(radius));
```

**Output of the above code-**

```
Enter the radius: 10
Area is 314.200000
```

## Python program to find area of circle using diameter

**Diameter** is the distance across the circle passing through the centre. We can also calculate the area of the circle if we know the diameter. Either, we can divide the diameter by 2 and calculate the area using the above process, like this.

```
# Program to calculate area of circle
def area_of_circle(r):
PI = 3.142
return PI * (r*r);
# get user input
diameter = float(input("Enter the diameter of a circle: "))
radius = diameter / 2
# print area of circle
print("Area is %.6f" % area_of_circle(radius));
```

**Output of the above code-**

```
Enter the diameter of a circle: 53
Area is 2206.469500
```

Or, we can use the following formula to calculate the area of the circle using diameter.

**A=π/4*D²**

Here is the program to calculate the area of the circle using the diameter. For this, we first imported the **math** module and then used the direct formula to calculate the area of the circle.

```
# Program to calculate area of circle
import math
diameter = float(input("Enter the diameter of a circle: "))
area = (math.pi/4) * (diameter * diameter)
print("Area of circle is %.2f" %area);
```

**Output of the above code -**

```
Enter the diameter of a circle: 23
Area of circle is 415.48
```

## Python program to find area of circle using circumference

The circle's circumference is the distance around the circle. We can easily calculate the area of a circle if we know the circumference using the formula **A= C²⁄ 4π**, where **C** is the circumference. The following program demonstrates this.

```
# Program to calculate area of circle
import math
circumference = float(input("Enter the circumference of a circle: "))
area = (circumference * circumference)/(4 * math.pi)
print("Area of circle is %.2f" %area);
```

**Output of the above code -**

```
Enter the circumference of a circle: 23
Area of circle is 42.10
```

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