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Converters

Temperature Converter

Temperature is the one category where conversion is not a simple multiplication — the scales are offset from one another, so 0 °C is 32 °F rather than 0 °F. The converter also refuses temperatures below absolute zero rather than returning a number that cannot exist.

degrees Celsius to degrees Fahrenheit

33.8 °F

1 °C converted

Conversion factor
Exact by definition

Worth knowing

  • Temperature scales are offset from one another, so conversions cannot be done by multiplication alone: 0 °C is 32 °F, not 0 °F.
  • Kelvin and Rankine are absolute scales with no negative values. A temperature below absolute zero is physically impossible, and the converter says so rather than returning a number.

How to use this tool

  1. Enter the temperature you want to convert.
  2. Choose the scale you are converting from and the one you want.
  3. The result appears immediately. Values below absolute zero are rejected with an explanation.

Formula and method

Celsius and Fahrenheit

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

The 9/5 accounts for the different degree sizes — a Celsius degree is 1.8 times a Fahrenheit degree — and the 32 accounts for the scales having different zero points.

Absolute scales

K = °C + 273.15
°R = °F + 459.67

Kelvin and Rankine start at absolute zero, the point where thermal motion stops. Neither has negative values.

Worked examples

Body temperature in Fahrenheit

  1. 37 × 9/5 = 66.6
  2. 66.6 + 32 = 98.6

37 °C is 98.6 °F.

The point where both scales agree

  1. (−40 × 9/5) + 32 = −72 + 32 = −40

−40 °C and −40 °F are the same temperature.

Notes and limitations

  • Temperature conversion cannot be done by multiplication alone, because the scales have different zero points. This is why there is no single 'conversion factor' shown for temperature pairs.
  • Absolute zero is −273.15 °C, −459.67 °F, 0 K and 0 °R. The converter rejects anything below it rather than returning an impossible figure.
  • A temperature *difference* converts differently from a temperature. A rise of 10 °C is a rise of 18 °F, not 50 °F — for differences, use the 9/5 ratio without the 32 offset.
  • Kelvin is written without a degree symbol: 300 K, not 300 °K.

Frequently asked questions

How do I convert Celsius to Fahrenheit?

Multiply by 9/5 and add 32. For a quick mental estimate, double it and add 30 — that gets you within a couple of degrees for everyday temperatures.

How do I convert Fahrenheit to Celsius?

Subtract 32, then multiply by 5/9. The subtraction has to come first; doing it in the other order gives a wrong answer.

At what temperature are Celsius and Fahrenheit equal?

At −40 degrees. It is the only point where the two scales give the same number.

Why can't I enter a temperature below −273.15 °C?

Because it does not exist. Absolute zero is the point at which molecular motion stops, and nothing can be colder. The converter says so instead of quietly returning a number.

Is 0 K the same as 0 °C?

No. 0 K is absolute zero, which is −273.15 °C. 0 °C is the freezing point of water, which is 273.15 K.

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