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Temperature Converter

Convert between Celsius, Fahrenheit and Kelvin. Unlike length or weight, temperature scales have different zero points, so the conversion involves both a multiplication and an offset.

How to use this converter

  1. Enter the temperature.
  2. Choose the scale you are converting from and the scale you want.
  3. Negative values are allowed, down to absolute zero.

Formula

°F = °C × 9/5 + 32 · °C = (°F − 32) × 5/9 · K = °C + 273.15

°C
degrees Celsius
°F
degrees Fahrenheit
K
kelvin, which takes no degree symbol

−40 is the single point where Celsius and Fahrenheit agree.

Worked example

Converting 37 °C, normal human body temperature, to Fahrenheit.

  1. Multiply37 × 9 ÷ 5 = 66.6
  2. Add offset66.6 + 32

37 °C is 98.6 °F, which is why the familiar body-temperature figure differs between the two scales.

Why temperature conversion is different

Length and mass units share a zero: zero metres is zero feet. Temperature scales do not. Zero Celsius is 32 Fahrenheit, and zero Kelvin is −273.15 Celsius. That means converting a temperature needs an offset as well as a scale factor.

It also means a temperature difference converts differently from a temperature. A rise of 10 °C is a rise of 18 °F, not 50 °F.

Absolute zero

Absolute zero, 0 K or −273.15 °C, is the lowest temperature physically possible. The calculator rejects values below it, because such a temperature cannot exist.

Things to keep in mind

  • Kelvin is written without a degree symbol: 300 K, not 300 °K.
  • Weather reports in India use Celsius; the United States uses Fahrenheit.

Frequently asked questions

What is a quick way to convert Celsius to Fahrenheit in my head?

Double the Celsius figure and add 30. For 20 °C that gives 70, against an exact answer of 68 °F. It is close enough for weather, though not for cooking or medicine.

At what temperature are Celsius and Fahrenheit the same?

At −40. Minus forty degrees Celsius is exactly minus forty degrees Fahrenheit.

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