Python Program to find the area of a circle

In this article, we will learn how to calculate the area of a circle using Python. Given the radius of a circle, we need to find its area using a simple mathematical formula.

The area of a circle can be calculated using the following formula ?

Area = ? × r²

Where ? (pi) is approximately 3.14159 and r is the radius of the circle.

Method 1: Using a Simple Function

Let's implement a basic function to calculate the area ?

def findArea(r):
    PI = 3.14159
    return PI * (r * r)

# Calculate area for radius = 5
radius = 5
area = findArea(radius)
print(f"Area of circle with radius {radius} is {area:.2f}")

Area of circle with radius 5 is 78.54

Method 2: Using the Math Module

For more precision, we can use the math.pi constant ?

import math

def calculate_circle_area(radius):
    return math.pi * radius ** 2

# Test with different radius values
radii = [3, 5, 7.5, 10]

for r in radii:
    area = calculate_circle_area(r)
    print(f"Radius: {r}, Area: {area:.4f}")

Radius: 3, Area: 28.2743
Radius: 5, Area: 78.5398
Radius: 7.5, Area: 176.7146
Radius: 10, Area: 314.1593

Method 3: Interactive Program

Here's a complete program that takes user input ?

import math

def get_circle_area():
    try:
        radius = float(input("Enter the radius of the circle: "))
        
        if radius < 0:
            print("Radius cannot be negative!")
            return None
        
        area = math.pi * radius ** 2
        return area
    
    except ValueError:
        print("Please enter a valid number!")
        return None

# Example usage (simulating user input)
radius = 6.5
area = math.pi * radius ** 2
print(f"For radius = {radius}")
print(f"Area = ? × {radius}² = {area:.6f} square units")

For radius = 6.5
Area = ? × 6.5² = 132.732229 square units

Comparison of Methods

Conclusion

Use math.pi for accurate circle area calculations in Python. The formula ? × r² works for any positive radius value. Always validate input to handle negative radius values appropriately.