Temperature converter

Convert a temperature between Celsius, Fahrenheit and Kelvin — useful for weather, cooking, science and travel.

How this calculator works

Celsius and Fahrenheit are both interval scales, but they start at different points and use different step sizes. Water freezes at 0 °C or 32 °F and boils at 100 °C or 212 °F, so 100 Celsius degrees span 180 Fahrenheit degrees — a ratio of 9/5. Kelvin uses the same step size as Celsius but starts at absolute zero, which is −273.15 °C, so a Kelvin temperature is simply Celsius plus 273.15.

Because of the offset, you cannot convert a temperature by scaling alone: the formula subtracts or adds the offset as well. A handy mental check is the crossover — −40 °C equals −40 °F — and that a normal body temperature of 37 °C is 98.6 °F. The calculator uses exact definitions (the Kelvin is defined by the Boltzmann constant; the degree sizes are exact multiples), so displayed values are correct to two decimals.

The formula

Always convert to Celsius (or Kelvin) first, then to the target unit. Absolute zero is 0 K, −273.15 °C and −459.67 °F.

Worked example

The default input of 100 Celsius (°C) is 100.00 °C, which is 212.00 °F and 373.15 K.

Common mistakes

• Scaling without the offset. Doubling Celsius does not double Fahrenheit. The 32° offset must be applied.
• Treating Kelvin as degrees. Kelvin is written without the degree symbol: 300 K, not 300 °K.
• Rounding before converting. Convert first, then round. Rounding 98.6 °F to 99 °F before converting shifts the Celsius result noticeably.