Temperature Converter
Instantly convert a temperature between Celsius, Fahrenheit, and Kelvin. Useful for cooking, science experiments, weather comparisons, and international travel.
About this calculator
Temperature is measured on three common scales. Celsius (°C) sets 0° at water's freezing point and 100° at boiling. Fahrenheit (°F) uses 32° and 212° for the same points. Kelvin (K) is an absolute scale starting at absolute zero (−273.15 °C), used in science. The conversion formulas are: °C → °F: F = (C × 9/5) + 32. °F → °C: C = (F − 32) × 5/9. °C → K: K = C + 273.15. K → °C: C = K − 273.15. °F → K: K = ((F − 32) × 5/9) + 273.15. K → °F: F = ((K − 273.15) × 9/5) + 32. All six paths are covered, so no matter which pair of units you choose the calculator applies the exact corresponding equation.
How to use
Example: convert 100 °C (boiling water) to Fahrenheit. Using F = (C × 9/5) + 32: F = (100 × 9/5) + 32 = (100 × 1.8) + 32 = 180 + 32 = 212 °F. Now convert the same temperature to Kelvin: K = 100 + 273.15 = 373.15 K. For a reverse example, convert 98.6 °F (normal body temperature) to Celsius: C = (98.6 − 32) × 5/9 = 66.6 × 5/9 = 37 °C. Select your starting unit, enter the value, choose your target unit, and the result appears instantly.
Frequently asked questions
What is the formula to convert Fahrenheit to Celsius quickly in my head?
A handy mental shortcut is to subtract 30 from the Fahrenheit value and then halve it, which gives a rough Celsius estimate. For example, 70 °F → (70 − 30) / 2 = 20 °C (exact answer: 21.1 °C). For precision, use the exact formula C = (F − 32) × 5/9. The approximation works well for everyday weather temperatures between about 0 °F and 100 °F, but drifts noticeably at extremes.
Why does the Kelvin scale start at absolute zero instead of water's freezing point?
Kelvin is an absolute thermodynamic scale anchored at absolute zero (0 K = −273.15 °C), the theoretical temperature at which all molecular motion ceases. Because it has no negative values, Kelvin is essential in physics, chemistry, and engineering equations — such as the ideal gas law (PV = nRT) — where a negative temperature would produce nonsensical results. The size of one Kelvin degree is identical to one Celsius degree, making conversions between the two trivially simple. Scientists and engineers prefer Kelvin whenever ratios of temperatures are physically meaningful.
When should I use Celsius versus Fahrenheit in everyday life?
Celsius is the standard in most countries and is used for weather, cooking, and medicine worldwide, except in the United States, which primarily uses Fahrenheit. For science and international communication, Celsius (or Kelvin) is always preferred. A practical rule: water freezes at 0 °C / 32 °F and boils at 100 °C / 212 °F — memorizing these two anchor points lets you sanity-check any conversion. For very precise scientific work, especially involving gases or thermodynamics, convert further to Kelvin.