Temperature Converter: Celsius, Fahrenheit, and Kelvin Explained

The Three Main Temperature Scales

Temperature is one of the most commonly converted units, yet the formulas are tricky enough that most people can't do them in their heads. Let's explore each scale and how to convert between them.

Celsius (C)

Used by most of the world, Celsius is based on water's properties: 0C is the freezing point of water, and 100C is the boiling point at sea level. Developed by Anders Celsius in 1742 (originally inverted, with 0 as boiling).

Fahrenheit (F)

Used primarily in the United States, Fahrenheit was created by Daniel Gabriel Fahrenheit in 1724. Water freezes at 32F and boils at 212F. The scale was based on three reference points: brine freezing (0F), water freezing (32F), and human body temperature (96F, later corrected to 98.6F).

Kelvin (K)

The SI unit of temperature, Kelvin starts at absolute zero (the coldest possible temperature, where molecular motion stops). 0K = -273.15C. Kelvin uses the same interval size as Celsius, so a 1K change equals a 1C change.

Conversion Formulas

// Celsius to Fahrenheit
F = (C * 9/5) + 32

// Fahrenheit to Celsius
C = (F - 32) * 5/9

// Celsius to Kelvin
K = C + 273.15

// Kelvin to Celsius
C = K - 273.15

// Fahrenheit to Kelvin
K = (F - 32) * 5/9 + 273.15

Quick Reference Points

Fun Fact

There's exactly one temperature where Celsius and Fahrenheit are equal: -40 degrees. At -40C = -40F. This is sometimes used as a quick sanity check for conversion formulas.

Programming Tip

When working with temperature in code, always store values in a standard unit (Celsius or Kelvin) and convert only for display. This avoids compounding rounding errors from repeated conversions.

Skip the mental math. Use the PureTools Temperature Converter for instant, accurate conversions between Celsius, Fahrenheit, and Kelvin.