Temperature Converter
This is the canonical temperature hub for converting among Celsius, Fahrenheit, and Kelvin. It is designed for mixed-scale work: a Celsius weather forecast compared with a Fahrenheit thermostat, a Fahrenheit oven note converted for an international recipe, or a Kelvin laboratory value translated into a more familiar reading. Choose the source scale, choose the target scale, and the calculator also shows the remaining scale as a reference so the result is easier to sanity-check.
Focused pages are still useful when the audience starts from one scale. Use the Celsius converter for a Celsius source with Fahrenheit, Kelvin, and Rankine outputs; the Celsius to Fahrenheit calculator for U.S. weather and cooking; the Kelvin converter for absolute-temperature source values; or the Kelvin to Fahrenheit converter for physics and engineering notes that need a Fahrenheit destination.
Formula
The component converts through Celsius. First it converts the source value to Celsius, then it converts Celsius to the requested target:
Celsius converts to itself with no change. The calculator validates the source value before converting: Celsius must be at least -273.15, Fahrenheit must be at least -459.67, and Kelvin must be at least 0.
Worked example: 20 °C to Fahrenheit
Select Celsius as the source, Fahrenheit as the target, and enter 20. The converter already has the value in Celsius, so it applies the Fahrenheit formula. Multiply 20 by nine fifths to get 36, then add 32. The result is 68 °F. The remaining scale is Kelvin, calculated by adding 273.15 to 20, which gives 293.15 K.
That matches the calculator’s display logic: the primary result is 68 °F, and the supporting item shows 293.15 for Kelvin. If you reverse the direction and enter 68 °F to Celsius, the converter subtracts 32, multiplies by five ninths, and returns 20 °C.
Reference table
| Celsius | Fahrenheit | Kelvin | Common meaning |
|---|---|---|---|
| -273.15 °C | -459.67 °F | 0 K | Absolute zero |
| -40 °C | -40 °F | 233.15 K | Celsius and Fahrenheit match |
| 0 °C | 32 °F | 273.15 K | Water freezes |
| 20 °C | 68 °F | 293.15 K | Comfortable room |
| 37 °C | 98.6 °F | 310.15 K | Approximate body temperature |
| 100 °C | 212 °F | 373.15 K | Water boils at sea level |
| 180 °C | 356 °F | 453.15 K | Common oven neighborhood |
The table mixes everyday and scientific anchors because this hub serves several audiences. Body temperature helps health and home users, the oven row helps cooking conversions, and absolute zero keeps the science boundary visible.
Scale definitions and history
Celsius is the everyday metric temperature scale. Its interval matches the kelvin, and its zero is 273.15 kelvin above absolute zero. Fahrenheit, associated with Daniel Gabriel Fahrenheit, remains common in the United States for weather, ovens, thermostats, and consumer thermometers. It places water freezing at 32 °F and boiling near 212 °F at standard pressure, creating 180 Fahrenheit intervals across the same water range that Celsius divides into 100.
Kelvin is the SI base unit for thermodynamic temperature. It starts at absolute zero and is written with the symbol K, not a degree symbol. The kelvin was defined using the triple point of water in 1954. In 2019, the SI redefinition fixed the numerical value of the Boltzmann constant, giving the unit a constant-based definition. The practical relationships used in this converter remain the familiar offsets: 0 °C is 273.15 K, and 0 K is -273.15 °C.
Choosing the right scale
Use Celsius for international weather, laboratory readings, storage instructions, and most product specifications. Use Fahrenheit for U.S. weather, home HVAC, cooking appliances, pool heaters, and familiar comfort descriptions. Use Kelvin when the calculation needs absolute temperature: ideal gases, thermodynamic efficiency, radiation, statistical mechanics, and many engineering formulas. The right choice depends less on the number itself and more on the audience and equation that will use it.
For weather effects rather than unit conversion, existing calculators such as heat index and wind chill may be more relevant. For heat as energy rather than temperature, use the energy converter.
Precision and pitfalls
Temperature conversion is offset-based. Do not use a single multiplier for actual readings. A 10 °C difference equals an 18 °F difference, but 10 °C as a temperature equals 50 °F. Likewise, 10 K as a temperature is extremely cold, while a change of 10 K has the same size as a change of 10 °C.
Keep Kelvin notation clean: 300 K, not 300 °K. Be careful near absolute zero; the converter rejects source values below the physical minimum for the selected scale. Round final answers to match the source measurement. A forecast may only justify whole degrees, while a lab instrument may justify decimals.
Sources
- NIST, SI Units — SI unit names and symbols.
- NIST, SI Units: Temperature — kelvin and Celsius relationships.
- BIPM, SI base units — official SI base-unit information.
- BIPM, SI defining constants — 2019 SI constant definitions.