Temperature Converter

The Kelvin is the SI base unit of thermodynamic temperature, defined by fixing the Boltzmann constant at exactly 1.380 649 × 10⁻²³ J/K. Celsius uses the same scale interval as Kelvin but is offset by 273.15 K. The Fahrenheit scale uses a 9/5 interval relative to Celsius and is offset by 32 °F. Rankine is the absolute temperature scale corresponding to Fahrenheit, used primarily in US engineering thermodynamics. Conversions involving Celsius or Fahrenheit often include an additive offset. Kelvin and Rankine share absolute zero, so K to °R requires only multiplication by 9/5.

All conversions in this category are computed relative to a single base unit (Celsius) using factors sourced from NIST Special Publication 811 and the BIPM SI Brochure. A shared reference unit keeps the conversion relationships consistent. Converting directly from the original measurement avoids the rounding differences that can accumulate when displayed intermediate results are entered again.

This calculator supports 4 units, including Celsius, Fahrenheit, Kelvin, Rankine. Choose the unit shown in your source measurement, then the unit needed for your result.

Units may have alternate spellings or abbreviations. You can search using these names too. Examples include Celsius (C, also written as celsius or centigrade), or Fahrenheit (F, also written as fahrenheit or °F), or Kelvin (K, also written as kelvin or °K).

Depending on the temperature pair, conversion may use a scale factor, an offset, or a reciprocal formula. Each converter page shows the formula for that pair, along with a worked example and a reference table.

Results and displayed coefficients are rounded for readability, usually to ten significant digits; very large or small results use scientific notation. Work from the original measurement and apply the rounding appropriate to its accuracy. A manual calculation using a displayed coefficient can differ slightly from the converter result.

Keep the unit alongside each temperature value when you copy or share it. Check that the source and target units match your task. If two units have similar names, read their definitions before selecting one.

For a second check, use the worked example and formula on the conversion page. Start from your original value rather than a rounded result from another calculator. If you need to report a specific number of decimal places, round once at the end.