Python Program to Convert Fahrenheit to Celsius

To convert Fahrenheit to Celsius in Python, use the formula C = (F - 32) * 5 / 9 where F is the Fahrenheit temperature and C is the Celsius temperature.

Examples

Input32

Output0.0

Input100

Output37.77777777777778

Input-40

Output-40.0

How to Think About It

To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit value to remove the offset, then multiply the result by 5/9 to scale it to the Celsius range. This formula adjusts the temperature from one scale to the other.

Algorithm

1

Get the temperature value in Fahrenheit from the user or input.

2

Subtract 32 from the Fahrenheit temperature.

3

Multiply the result by 5.

4

Divide the product by 9 to get the Celsius temperature.

5

Return or print the Celsius temperature.

Code

python

fahrenheit = float(input("Enter temperature in Fahrenheit: "))
celsius = (fahrenheit - 32) * 5 / 9
print(f"Temperature in Celsius: {celsius}")

Output

Enter temperature in Fahrenheit: 100
Temperature in Celsius: 37.77777777777778

Dry Run

Let's trace the input 100 Fahrenheit through the code

1

Input Fahrenheit

fahrenheit = 100.0

2

Subtract 32

100.0 - 32 = 68.0

3

Multiply by 5

68.0 * 5 = 340.0

4

Divide by 9

340.0 / 9 = 37.77777777777778

5

Print Celsius

Temperature in Celsius: 37.77777777777778

Step	Operation	Result
1	Input Fahrenheit	100.0
2	100.0 - 32	68.0
3	68.0 * 5	340.0
4	340.0 / 9	37.77777777777778
5	Print result	37.77777777777778

Why This Works

Step 1: Remove Fahrenheit offset

Subtracting 32 from the Fahrenheit value adjusts the starting point to zero Celsius.

Step 2: Scale the temperature

Multiplying by 5 and dividing by 9 converts the temperature scale from Fahrenheit to Celsius.

Step 3: Output the result

The final value is the temperature in Celsius, which can be printed or used further.

Alternative Approaches

Using a function

python

def fahrenheit_to_celsius(f):
    return (f - 32) * 5 / 9

print(fahrenheit_to_celsius(100))

This approach makes the conversion reusable and cleaner for multiple inputs.

Using lambda expression

python

convert = lambda f: (f - 32) * 5 / 9
print(convert(100))

A concise way to define the conversion inline, useful for quick calculations.

Complexity: O(1) time, O(1) space

Time Complexity

The calculation uses a fixed number of arithmetic operations, so it runs in constant time.

Space Complexity

Only a few variables are used, so the space needed is constant.

Which Approach is Fastest?

All approaches run in constant time; using a function or lambda improves code reuse but does not affect speed.

Approach	Time	Space	Best For
Direct calculation	O(1)	O(1)	Simple one-time conversion
Function	O(1)	O(1)	Reusable code for multiple conversions
Lambda	O(1)	O(1)	Quick inline conversions