Celsius to Fahrenheit Formula in Excel and Code

The formula in one line

F = C × 9/5 + 32  ·  C = (F − 32) × 5/9

In code, the main thing to watch is integer division. In languages like Java, C and C++, writing 9/5 with two whole numbers gives 1, not 1.8, and every result will be wrong. Use floating-point literals (9.0/5.0) or multiply before dividing (c * 9 / 5 with c already a double). Python 3 and JavaScript always do true division, so 9/5 is safe there.

Round only when you display a value, not in the middle of a calculation. Rounding early can push a result off by 0.01 or more after a few steps.

Code snippets

Excel

Celsius in cell A1:

=A1*9/5+32
=CONVERT(A1,"C","F")

' Fahrenheit in A1 back to Celsius:
=(A1-32)*5/9
=CONVERT(A1,"F","C")

' Rounded to 2 decimals:
=ROUND(A1*9/5+32,2)

Google Sheets

Same formulas work in Google Sheets; CONVERT supports C, F and K:

=A1*9/5+32
=CONVERT(A1,"C","F")
=(A1-32)*5/9
=CONVERT(A1,"C","K")

// Whole column at once (A2:A):
=ARRAYFORMULA(IF(A2:A="",,A2:A*9/5+32))

Python

def c_to_f(c: float) -> float:
    return c * 9 / 5 + 32

def f_to_c(f: float) -> float:
    return (f - 32) * 5 / 9

print(round(c_to_f(37), 2))   # 98.6
print(round(f_to_c(350), 2))  # 176.67

JavaScript

const cToF = (c) => c * 9 / 5 + 32;
const fToC = (f) => (f - 32) * 5 / 9;

console.log(cToF(100));               // 212
console.log(fToC(350).toFixed(2));    // "176.67"

Java

public class TempConvert {
    static double cToF(double c) { return c * 9.0 / 5.0 + 32.0; }
    static double fToC(double f) { return (f - 32.0) * 5.0 / 9.0; }

    public static void main(String[] args) {
        System.out.printf("%.2f%n", cToF(25));   // 77.00
        System.out.printf("%.2f%n", fToC(98.6)); // 37.00
    }
}

C

#include <stdio.h>

double c_to_f(double c) { return c * 9.0 / 5.0 + 32.0; }
double f_to_c(double f) { return (f - 32.0) * 5.0 / 9.0; }

int main(void) {
    printf("%.2f\n", c_to_f(-40.0)); /* -40.00 */
    printf("%.2f\n", f_to_c(212.0)); /* 100.00 */
    return 0;
}

C++

#include <iostream>
#include <iomanip>

double cToF(double c) { return c * 9.0 / 5.0 + 32.0; }
double fToC(double f) { return (f - 32.0) * 5.0 / 9.0; }

int main() {
    std::cout << std::fixed << std::setprecision(2);
    std::cout << cToF(180) << "\n";  // 356.00
    std::cout << fToC(0) << "\n";    // -17.78
}

Tips for spreadsheets

Excel's CONVERT function understands "C", "F", "K" and "Rank" (Rankine), so =CONVERT(A1,"K","F") converts Kelvin to Fahrenheit directly. Unit codes are case-sensitive: "c" will return an error. If you prefer to see the maths, the plain formula version is easier to audit and works identically in LibreOffice and Google Sheets.

To build a conversion table, put a starting value in A2, enter =A2+1 in A3 and fill down, then put =A2*9/5+32 in B2 and fill down. Format column B with two decimal places. If you just need a ready-made table, the printable Celsius to Fahrenheit chart already has one.

Formula in Roman Urdu / Hindi

Test values for your code

Use unrounded values for calculation tests, then test the formatted display separately. These pairs cover the freezing and boiling points, the crossover at −40, and repeating decimals:

• 0 °C → 32 °F and 100 °C → 212 °F
• −40 °C → −40 °F (the two scales are equal)
• 37 °C → 98.6 °F
• 350 °F → 530/3 °C (about 176.6666667 °C); display: 176.67 °C
• 0 °F → −160/9 °C (about −17.7777778 °C); display: −17.78 °C

For these small test values, compare the unrounded calculation with a tolerance such as 1e-9. Do not compare it with a rounded display value: the correct result for 350 °F differs from 176.67 by about 0.00333. Choose a tolerance appropriate to the values and precision your application needs.

const fToC = (f) => (f - 32) * 5 / 9;

// Unrounded calculations:
console.assert(Math.abs(fToC(350) - 530 / 3) < 1e-9);
console.assert(Math.abs(fToC(0) - (-160 / 9)) < 1e-9);

// Display formatting is a separate test:
console.assert(fToC(350).toFixed(2) === "176.67");
console.assert(fToC(0).toFixed(2) === "-17.78");

Floating-point values such as 98.6 cannot be represented exactly in binary. Use a tolerance for calculation tests and compare formatted strings for display tests. To check any other value, use the Celsius to Fahrenheit converter or Kelvin converter.