Temperature Converter
Convert between Celsius, Fahrenheit and Kelvin. Unlike length or mass, temperature scales cannot be converted by multiplying alone, because they place their zero points at different physical temperatures. Each conversion here applies both a scaling factor and an offset.
How to use this tool
- Enter the temperature in the Value field. Negative values are expected and handled correctly.
- Choose the scale your reading is currently in.
- Choose the scale you want it converted to.
- The answer updates as you type.
- If you enter something below absolute zero, the converter will say so rather than returning a meaningless negative Kelvin figure.
The formula
Temperature scales cannot be converted by a single ratio because their zero points differ. Celsius and Fahrenheit place zero at different physical temperatures, so each conversion needs both a scaling factor and an offset.
°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- 9/5
- A Fahrenheit degree is 5/9 the size of a Celsius degree
- 32
- Fahrenheit places water’s freezing point at 32, not 0
- 273.15
- Celsius degrees between absolute zero and water’s freezing point
Absolute zero is −273.15 °C, −459.67 °F or 0 K. Nothing can be colder, so this converter rejects temperatures below it.
Worked examples
A comfortable room temperature
- Given
- 20 °C
- Result
- 68 °F
20 × 9/5 = 36, then 36 + 32 = 68 °F. The multiplication accounts for Fahrenheit degrees being smaller; the addition accounts for its different zero point.
Oven temperature from a US recipe
- Given
- 350 °F
- Result
- 176.666667 °C
(350 − 32) = 318, then 318 × 5/9 = 176.67 °C. Most ovens would be set to 180 °C, the nearest standard mark.
The point where both scales agree
- Given
- −40 °C
- Result
- −40 °F
Setting C = C × 9/5 + 32 and solving gives C = −40. This is the single temperature at which the Celsius and Fahrenheit scales read the same, which makes it a useful check that a conversion is working.
Frequently asked questions
That is absolute zero, the point at which a system has no thermal energy left to remove. Nothing can be colder, so a lower value does not describe a very cold object — it describes nothing at all. The converter rejects it rather than reporting a negative Kelvin figure that looks like an answer.
Kelvin is an absolute scale, so its unit is the kelvin rather than a degree of anything. The correct form is 300 K, not 300 °K. The degree symbol was officially dropped in 1967.
Differences convert using only the scaling factor, without the offset. A rise of 10 °C is a rise of 18 °F, not 50 °F. This converter handles readings, which is what most people need; for a difference, multiply by 9/5 going to Fahrenheit or by 5/9 coming back.
Effectively yes. Centigrade was the original name, meaning a hundred steps between the freezing and boiling points of water. It was renamed after Anders Celsius in 1948, partly because centigrade already meant a hundredth of a right angle in some languages.
Water freezes at 0 °C, 32 °F or 273.15 K, and boils at sea level at 100 °C, 212 °F or 373.15 K. Normal human body temperature is about 37 °C or 98.6 °F. Absolute zero is −273.15 °C, −459.67 °F or 0 K.
It is an artefact of conversion. The original nineteenth-century measurement was 37 °C, given to two significant figures. Converting that produces 98.6 °F, which looks far more precise than the underlying measurement ever was. Body temperature actually varies by roughly half a degree Celsius through the day.
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