# How to Find Area of a Circle with Diameter in Python | Functions

How to find area of a circle with diameter in Python using functions.

In this article, you will learn how to find area of a circle with diameter in Python using functions.

### Example

**Enter the radius of the circle::
10**

**Diameter = 20.0 units
Circumference = 62.800000000000004 units
Area = 314.0 sq. units**

### Standard Formula

`D = 2 * r`

`C = 2 * PI * r`

`A = PI * r2`

`r = radius of the circle`

`D = diameter of the circle`

`C = circumference of the circle`

`A = area of the circle`

You should have knowledge of the following topics in Python programming to understand this program:

- Python

function**input()**

### 1. By using the default value of **PI = 3.14**

```
# How to Find Area of a Circle with Diameter in Python
print("Enter the radius of the circle::\n")
r, d, c, a = float(input()), None, None, None
# r = radius, d = diameter, c = circumference, a = area
# It will calculate the diameter, circumference, and area
d = 2 * r
c = 2 * 3.14 * r
a = 3.14 * (r * r)
# It will print the final output
print("Diameter = ", d, "units")
print("Circumference = ", c, "units")
print("Area = ", a, " sq. units")
```

### Output

`Enter the radius of the circle::`

10

`Diameter = 20.0 units`

Circumference = 62.800000000000004 units

Area = 314.0 sq. units

### Explanation

In the above program, we have taken input

from the user via the system console. Then we applied the standard formula to calculate the diameter, circumference, and area.**10**

Standard formulas are given at the top of the article near the example portion can see there.

After the whole calculation, It will return these values following:

- Diameter =
**20.0 units** - Circumference =
**62.800000000000004 units** - Area =
**314.0 sq. units**

### 2. By using **Math.PI** constant

```
# How to Find Area of a Circle with Diameter in Python using math.pi constant
# Import math Library
import math
print("Enter the radius of the circle::\n")
r, d, c, a = float(input()), None, None, None
# r = radius, d = diameter, c = circumference, a = area
# It will calculate the diameter, circumference, and area
d = 2 * r
c = 2 * math.pi * r
a = math.pi * (r * r)
# It will print the final output
print("Diameter = ", d, "units")
print("Circumference = ", c, "units")
print("Area = ", a, " sq. units")
```

### Output

`Enter the radius of the circle::`

10

`Diameter = 20.0 units`

Circumference = 62.83185307179586 units

Area = 314.1592653589793 sq. units

## How to Find Area of a Circle with Diameter in Python using Functions

```
# How to Find Area of a Circle with Diameter in Python using Functions
# To calculate the diameter
def Diameter(r):
return 2 * r
# To calculate the circumference
def Circumference(r):
return 2 * 3.14 * r
# To calculate the area
def Area(r):
return 3.14 * (r * r)
# It's the driver code
print("Enter the radius of the circle::\n")
r = float(input()) # r = radius
# It will print the final output
print("Diameter = ", Diameter(r), "units")
print("Circumference = ", Circumference(r), "units")
print("Area = ", Area(r), " sq. units")
```