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Free Online Temperature Converter

Convert between Celsius, Fahrenheit, and Kelvin with the exact formula displayed.

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Formula—

How Temperature Conversion Works

Unlike most unit conversions that use a simple multiplication factor, temperature conversion involves both multiplication and addition because the three scales have different zero points. Celsius and Kelvin share the same degree size but are offset by 273.15. Fahrenheit uses a different degree size (9/5 of a Celsius degree) and a different zero point. This tool uses the exact formulas below to ensure accurate conversion every time.

Temperature Conversion Formulas

ConversionFormula
Celsius to Fahrenheit°F = (°C × 9/5) + 32
Fahrenheit to Celsius°C = (°F − 32) × 5/9
Celsius to KelvinK = °C + 273.15
Kelvin to Celsius°C = K − 273.15
Fahrenheit to KelvinK = (°F − 32) × 5/9 + 273.15
Kelvin to Fahrenheit°F = (K − 273.15) × 9/5 + 32

Key Temperature Reference Points

PointCelsiusFahrenheitKelvin
Absolute Zero−273.15−459.670
Water Freezes032273.15
Human Body3798.6310.15
Water Boils100212373.15

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Frequently Asked Questions

Why can't temperature be converted with a simple multiplication factor?
Temperature scales have different zero points and degree sizes. Celsius and Fahrenheit, for example, differ in both where zero is set and how large each degree is, so the formula requires both multiplication and addition.
What is absolute zero?
Absolute zero is 0 Kelvin (-273.15°C or -459.67°F). It is the lowest possible temperature, where all molecular motion stops.
How do I quickly estimate Celsius to Fahrenheit?
A quick approximation: double the Celsius value and add 30. For example, 20°C ≈ (20×2)+30 = 70°F (actual: 68°F). This works reasonably well for everyday temperatures.
At what temperature are Celsius and Fahrenheit equal?
Celsius and Fahrenheit are equal at -40 degrees. That is, -40°C = -40°F.
Is my data stored anywhere?
No. All conversions happen entirely in your browser. No data is transmitted to any server.