Temperature Converter: Celsius, Fahrenheit and Kelvin
Converting temperature means handling two different scale sizes and two different zero points. Celsius and Kelvin share a degree size, Fahrenheit degrees are smaller, and only Kelvin starts at absolute zero.
The conversion formulas
- °F = (°C × 9/5) + 32
- °C = (°F − 32) × 5/9
- K = °C + 273.15
- °C = K − 273.15
Reference points to sanity-check a result
- Water freezes at 0 °C / 32 °F / 273.15 K.
- Water boils at 100 °C / 212 °F / 373.15 K at sea level.
- Normal body temperature is about 37 °C / 98.6 °F.
- −40 is the one temperature where Celsius and Fahrenheit read the same.
Why Kelvin exists
Kelvin is an absolute scale: 0 K is absolute zero, the point where thermal motion is minimal, so it has no negative values. That makes it the scale used in physics and chemistry, where gas laws and thermodynamic equations depend on ratios of temperature. Doubling temperature only means something on an absolute scale — 20 °C is not twice as hot as 10 °C.
Quick mental approximation
To go from Celsius to Fahrenheit roughly, double it and add 30: 20 °C gives about 70 °F against an exact 68 °F. Going the other way, subtract 30 and halve. It is close enough for weather and travel, though never for cooking, medical or scientific use.
Key takeaways — Temperature Converter
- Fahrenheit conversions need both a scaling factor and a 32-degree offset.
- Kelvin equals Celsius plus 273.15 and never goes negative.
- Use exact formulas for anything scientific, medical or culinary.