Temperature Converter – Celsius to Fahrenheit & Kelvin

Convert temperatures between Celsius, Fahrenheit, and Kelvin instantly with our free online temperature converter. Get accurate conversions with the formula used shown clearly.

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Understanding Temperature Scales

Temperature measures how hot or cold something is, but different scales use different reference points. Celsius sets 0° at water's freezing point and 100° at boiling. Fahrenheit uses 32° for freezing and 212° for boiling. Kelvin starts at absolute zero – the coldest possible temperature where molecular motion stops.

Scientists use Kelvin because it's an absolute scale with no negative values. Weather forecasters use Celsius or Fahrenheit depending on the country. Cooking recipes might use any of the three. This converter handles all the math so you can focus on what matters.

Temperature Conversion Formulas

Celsius to Fahrenheit

°F = (°C × 9/5) + 32

Example: 20°C = (20 × 1.8) + 32 = 68°F

Fahrenheit to Celsius

°C = (°F - 32) × 5/9

Example: 68°F = (68 - 32) × 5/9 = 20°C

Celsius to Kelvin

K = °C + 273.15

Example: 25°C = 25 + 273.15 = 298.15 K

Kelvin to Celsius

°C = K - 273.15

Example: 300 K = 300 - 273.15 = 26.85°C

Worked Examples

Example 1: Body temperature

Problem: Convert normal body temperature 98.6°F to Celsius

Solution: °C = (98.6 - 32) × 5/9 = 66.6 × 5/9

°C = 333/9 = 37°C. Normal body temperature is 37°C.

Example 2: Oven temperature

Problem: A recipe calls for 180°C. What's that in Fahrenheit?

Solution: °F = (180 × 9/5) + 32 = 324 + 32

°F = 356°F. Set your oven to 350-360°F.

Example 3: Absolute zero

Problem: What is absolute zero (0 K) in Celsius and Fahrenheit?

Solution: °C = 0 - 273.15 = -273.15°C

°F = (-273.15 × 9/5) + 32 = -459.67°F. The coldest possible temperature.

Example 4: Room temperature

Problem: Convert comfortable room temperature 20°C to all scales

Solution: °F = (20 × 9/5) + 32 = 36 + 32 = 68°F

K = 20 + 273.15 = 293.15 K. Room temperature is 20°C / 68°F / 293.15 K.

Example 5: The -40 coincidence

Problem: At what temperature are Celsius and Fahrenheit equal?

Solution: Set °C = °F = x. Then x = (x × 9/5) + 32

x - 9x/5 = 32 → -4x/5 = 32 → x = -40

-40°C = -40°F. The only temperature where both scales read the same!

Quick Fact

Daniel Fahrenheit originally defined 0°F as the temperature of a brine solution (ice, water, and ammonium chloride). He set 96°F as human body temperature (later adjusted to 98.6°F). Anders Celsius originally defined 0° as boiling and 100° as freezing – the reverse of today's scale! It was flipped after his death for intuitive sense.

Temperature Reference Points

Phenomenon	Celsius	Fahrenheit	Kelvin
Absolute zero	-273.15°C	-459.67°F	0 K
Water freezes	0°C	32°F	273.15 K
Room temperature	20°C	68°F	293.15 K
Body temperature	37°C	98.6°F	310.15 K
Water boils	100°C	212°F	373.15 K
Surface of Sun	5,500°C	9,932°F	5,773 K

Frequently Asked Questions

Why does Fahrenheit seem so arbitrary?

Fahrenheit's scale was based on practical reference points available in 1724: 0°F was the coldest temperature he could reliably reproduce (brine solution), 32°F was water's freezing point, and 96°F was body temperature. The scale was designed for everyday use, not scientific elegance.

Why is Kelvin used in science?

Kelvin is an absolute scale starting at absolute zero. This makes equations simpler – no negative temperatures to worry about. Gas laws, thermodynamics, and quantum mechanics all work more cleanly with Kelvin. One Kelvin degree equals one Celsius degree.

How do I convert quickly without a calculator?

For °C to °F: Double the Celsius, subtract 10%, add 32. For 20°C: 20×2=40, 40-4=36, 36+32=68°F. For °F to °C: Subtract 32, halve, add 10%. For 68°F: 68-32=36, 36/2=18, 18+2=20°C. Close enough for weather!

What's the coldest temperature possible?

Absolute zero: 0 K, -273.15°C, or -459.67°F. At this temperature, all molecular motion stops (classically). Quantum mechanics says there's still zero-point energy, but you can't get colder. Scientists have reached within billionths of a degree of absolute zero in labs.

Why 273.15 specifically?

The value comes from the triple point of water – where ice, liquid, and vapor coexist. This occurs at exactly 0.01°C or 273.16 K. The offset is defined so that absolute zero is exactly -273.15°C. It's a measured physical constant, not an arbitrary number.

Which countries use Fahrenheit?

Only the United States, its territories, and a few Caribbean nations (Bahamas, Cayman Islands) use Fahrenheit for everyday temperatures. Everyone else uses Celsius. Scientists worldwide use Kelvin for research and Celsius for most applications.

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