Unit converter

Fahrenheit to Celsius.

Convert °F to °C and °C to °F. Type in either box and the other follows. Subtract 32 first, then multiply by five ninths. Doing it the other way round is the classic wrong answer.

From

°F → °CExact definition

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Display precision

Degrees Fahrenheit to degrees Celsius — common values, to 6 significant figures.
°F	°C
−40 °F	−40 °C
−20 °F	−28.8889 °C
0 °F	−17.7778 °C
10 °F	−12.2222 °C
20 °F	−6.66667 °C
32 °F	0 °C
50 °F	10 °C
68 °F	20 °C
86 °F	30 °C
98.6 °F	37 °C
100 °F	37.7778 °C
150 °F	65.5556 °C
212 °F	100 °C

°C = \frac{5}{9} \times (°F - 32)

°F = °C \times \frac{9}{5} + 32

Both scales are fixed against the kelvin, so the conversion is a stretch and a shift, applied in that order.

Definitions

Fahrenheit puts water's freezing point at 32 and its boiling point at 212, so a Fahrenheit degree is five ninths of a Celsius one.
Celsius puts 0 at the freezing point of water and 100 at its boiling point at standard pressure. A Celsius degree is the same size as a kelvin.
This conversion is exact by definition. °C = °F × 0.5555555556 − 17.77777778.
Temperature scales have different zero points, so conversion is a scale AND a shift. A temperature and a temperature difference do not convert the same way.

How it works

The two scales differ in step size and in where they start counting, so the conversion applies a scale and a shift — and the order matters. Reversing it means undoing the shift first, then the scale.

The value passes through K, the unit every other temperature unit on the site is defined against, rather than a number written into this page on its own. That is why the figure here, the figure in the table above and the general temperature converter always agree.

Display precision limits significant figures rather than decimal places, so a reading near zero keeps its detail instead of collapsing to one digit. Rounding is applied to the large display only, never to the arithmetic behind it. The editable box always holds a plain number at full working precision, so you can carry on from either side.

Common questions this answers: what 20 °F is in degrees Celsius (−6.66667 °C), what 0 °F is (−17.7778 °C), and why a rise of 10 °F is a rise of 5.55556 °C, not −12.2222.

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