Celsius to Fahrenheit: Formula, Chart, and Converter

Celsius and Fahrenheit describe the same physical reality — how hot or cold something is — but they use completely different numbers. 100°C is boiling water. 212°F is also boiling water. Same thing, different scales.

Here's the formula, a reference chart, and the context you need to stop being confused.

The formula

Celsius → Fahrenheit:

°F = (°C × 9/5) + 32

Fahrenheit → Celsius:

°C = (°F − 32) × 5/9

Example: 25°C to Fahrenheit

°F = (25 × 9/5) + 32
°F = (225/5) + 32
°F = 45 + 32
°F = 77°F

Example: 98.6°F to Celsius (body temperature)

°C = (98.6 − 32) × 5/9
°C = 66.6 × 5/9
°C = 333/9
°C = 37°C

Quick mental shortcuts

If you need a rough conversion in your head:

°C to °F: Double it, subtract 10%, add 32.

• 20°C → double = 40, minus 10% = 36, plus 32 = 68°F (actual: 68°F ✓)
• 30°C → double = 60, minus 10% = 54, plus 32 = 86°F (actual: 86°F ✓)

°F to °C: Subtract 30, halve it.

• 80°F → minus 30 = 50, halve = 25°C (actual: 26.7°C — close enough for everyday use)
• 50°F → minus 30 = 20, halve = 10°C (actual: 10°C ✓)

These aren't exact, but they're accurate enough for "what should I wear today."

Temperature reference chart

Conversion in code

JavaScript:

function celsiusToFahrenheit(c) {
  return (c * 9/5) + 32;
}

function fahrenheitToCelsius(f) {
  return (f - 32) * 5/9;
}

console.log(celsiusToFahrenheit(100)); // 212
console.log(fahrenheitToCelsius(32));  // 0

Python:

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

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

print(celsius_to_fahrenheit(100))  # 212.0
print(fahrenheit_to_celsius(32))   # 0.0

Go:

func CelsiusToFahrenheit(c float64) float64 {
    return (c * 9.0 / 5.0) + 32
}

func FahrenheitToCelsius(f float64) float64 {
    return (f - 32) * 5.0 / 9.0
}

PHP:

function celsiusToFahrenheit(float $c): float {
    return ($c * 9/5) + 32;
}

function fahrenheitToCelsius(float $f): float {
    return ($f - 32) * 5/9;
}

echo celsiusToFahrenheit(100); // 212
echo fahrenheitToCelsius(32);  // 0

What about Kelvin?

Kelvin is the third major temperature scale, used in science and physics. Unlike Celsius and Fahrenheit, Kelvin has no negative values — 0 K (absolute zero) is the coldest anything can possibly be.

Celsius → Kelvin:

K = °C + 273.15

Kelvin → Celsius:

°C = K − 273.15

Water freezes at 273.15 K and boils at 373.15 K. Room temperature is about 293–296 K.

You rarely need Kelvin in everyday life, but it shows up in physics equations, astronomy, and engineering contexts (gas laws, radiation formulas, etc.).

Why do two scales exist?

Celsius (originally "centigrade") was proposed by Anders Celsius in 1742. He defined the scale with 0 as the boiling point and 100 as the freezing point of water — which was then reversed to the current convention. It's intuitive: 0 is freezing, 100 is boiling, human comfort is in the 20–25 range.

Fahrenheit was developed by Daniel Gabriel Fahrenheit in 1724. He originally anchored his scale to three reference points: the freezing point of a brine solution (0°F), the freezing point of water (32°F), and human body temperature (which he measured as 96°F — slightly off from the modern 98.6°F). The result is a scale where everyday outdoor temperatures fall in the 0–100°F range in most populated areas.

Most of the world uses Celsius. The United States, a few Caribbean islands, and some island nations use Fahrenheit. In science, Kelvin is standard.

Convert temperatures online

If you need to convert temperatures without doing the math by hand, use the Temperature Converter. Supports Celsius, Fahrenheit, and Kelvin. Runs entirely in your browser.

FAQ

Q: At what temperature is Celsius equal to Fahrenheit? At −40°. Both scales converge at exactly −40°C = −40°F. This is because the formula °F = (°C × 9/5) + 32 has a solution at −40.

Q: What is 37°C in Fahrenheit? 37°C = 98.6°F — normal human body temperature. A fever is generally considered 38°C (100.4°F) or higher.

Q: What is 0°F in Celsius? 0°F = −17.78°C. Fahrenheit's zero was based on the freezing point of a saturated salt solution, not plain water.

Q: Why is 72°F considered the ideal room temperature? 72°F (22.2°C) is a common target for office and home HVAC systems because studies have shown it's where most people feel thermally neutral without heavy clothing. The comfortable range is generally considered 68–76°F (20–24°C).