Kelvin shares Celsius degree size but starts at absolute zero, so K = °C + 273.15. Nothing in weather or cooking needs it.

Converters Temperature

Celsius to Fahrenheit

Celsius

Fahrenheit 68

Decimals

Live · °F = °C × 1.8 + 32

Temperatures worth recognising

-40 °C -40 °F

0 °C 32 °F

10 °C 50 °F

20 °C 68 °F

30 °C 86 °F

37 °C 98.6 °F

100 °C 212 °F

To convert Celsius to Fahrenheit, multiply by 1.8 and add 32. Water freezes at 0 °C or 32 °F and boils at 100 °C or 212 °F. Normal body temperature, 37 °C, is 98.6 °F. The two scales read the same at −40, which is the only temperature where no conversion is needed.

How to convert °C to °F

1 Enter the temperature in Celsius, negatives included.

2 Read the Fahrenheit value. The offset of 32 is applied for you.

3 Press ⇄ to convert Fahrenheit back to Celsius.

Temperature is the one everyday conversion that is not a simple multiplication, because the two scales do not share a zero. That is also why you cannot convert a temperature difference the same way: a rise of 10 °C is a rise of 18 °F, not 50 °F. Multiply differences by 1.8 and leave the 32 alone.

Questions

What is the quickest mental version? −

Double the Celsius and add 30. Twenty becomes 70 against a true 68, and 30 becomes 90 against 86. Close enough for weather, wrong for an oven.

Why is body temperature 98.6 °F such an odd number? +

Is Celsius the same as centigrade? +

When do the two scales agree? +

What about Kelvin? +

Sources

NIST — SI units: temperature BIPM — The International System of Units (SI)

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