Temperature Converter

Three temperature scales dominate: Celsius (°C), Fahrenheit (°F), and Kelvin (K). Celsius is used worldwide for weather and everyday life; it sets water's freezing point at 0°C and boiling point at 100°C. Fahrenheit, used mainly in the US, sets water freezing at 32°F and boiling at 212°F. Kelvin is the SI unit for temperature and starts at absolute zero (0 K = -273.15°C); it has no degree symbol and is used in science.

Each scale uses the same concept — temperature as a measure of thermal energy — but with different reference points and step sizes. Converting between them requires simple formulas that this tool applies instantly.

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.

These formulas are linear transformations. The Celsius-Kelvin relationship is a simple offset (273.15). The Celsius-Fahrenheit relationship involves both scaling (9/5) and offset (32) because the two scales use different zero points and different degree sizes.

Kelvin is the standard in physics, chemistry, and engineering because it is an absolute scale — zero Kelvin means zero thermal energy. Thermodynamic equations (e.g., ideal gas law, Boltzmann distribution) use Kelvin. When working with temperature differences, 1 K = 1°C, so the math is often interchangeable.

In meteorology and HVAC, Celsius and Fahrenheit are both used depending on region. Data loggers, sensors, and control systems may output in any of the three scales; conversion is essential when integrating systems or comparing data from different sources.

Daniel Fahrenheit invented his scale in 1724, originally using brine (salt water) freezing as 0°F and human body temperature as 96°F. Anders Celsius proposed his scale in 1742, with 0°C for water boiling and 100°C for freezing — the scale was later inverted. Lord Kelvin defined the absolute scale in 1848, establishing 0 K as the point at which all molecular motion ceases.

Today, the Kelvin is defined by the Boltzmann constant, linking it to the joule. The Celsius scale is defined relative to Kelvin: 0°C = 273.15 K exactly. This ensures consistency across scientific disciplines worldwide.