Contents
How the converter works
To convert Fahrenheit to Celsius, subtract 32 and divide by 1.8. The converter starts in that direction, accepts negative and decimal values, and can swap between Fahrenheit, Celsius, Kelvin, and Réaumur.
The 32-degree offset comes before the scale change
Fahrenheit and Celsius have different zero points and different degree sizes. Subtracting 32 aligns the zero points; dividing by 1.8 adjusts the interval. The reverse calculation is .
The conversion equations and the familiar 32 °F = 0 °C reference point are listed by the US National Institute of Standards and Technology.
Both number fields are editable
Enter a value in either field. Changing the left field recalculates the right one, while editing the right field works backward. Use the middle button to swap the two scales. The result is rounded to at most two decimal places, so a display such as 21.11 °C is practical without implying extra precision.
Three reference temperatures worth remembering
32 °F becomes 0 °C. This is the standard freezing reference for water. The calculation is (32 - 32) / 1.8 = 0.
68 °F becomes 20 °C. Subtracting 32 gives 36, and 36 / 1.8 = 20. This is a useful indoor-temperature checkpoint.
98.6 °F becomes 37 °C. The calculation gives 66.6 / 1.8 = 37. This familiar pair also shows why one decimal place in Fahrenheit can map to a whole Celsius value.
A conversion does not improve the measurement
If the source thermometer is accurate only to the nearest degree, extra decimals in the converted value do not make it more accurate. For laboratory work, keep the unrounded value through the calculation and round only at the end.
Values below 0 K, equal to -273.15 °C or -459.67 °F, are below absolute zero and have no physical temperature meaning. The calculator still performs the arithmetic, so the user must judge whether an entered value is physically possible.
Fahrenheit conversion questions
The most common mistakes involve the 32-degree offset, rounding, and temperature differences.
At what temperature are Fahrenheit and Celsius equal?
They show the same number at -40 degrees: -40 °F equals -40 °C.
Can I estimate Celsius quickly?
For a rough everyday estimate, subtract 30 and divide by 2. Use the exact formula for a reliable result.
Is a change of 1 °F the same as a change of 1 °C?
No. A Celsius degree interval is 1.8 times a Fahrenheit degree interval, so a 9 °F change equals a 5 °C change.
Why does the converter include Kelvin and Réaumur?
The selectors preserve the broader Ecalc converter: you can use the same two fields for four temperature scales.
Does water always boil at 212 °F?
No. 212 °F equals 100 °C as the standard reference at normal atmospheric pressure; the boiling point changes with pressure.
Similar calculators
You may find the following calculators on the same topic useful:
- Réaumur to Celsius Converter. Convert whole, negative, or decimal Réaumur values to Celsius and reverse the calculation from either field.
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- Celsius to Fahrenheit Converter. Convert negative, whole, or decimal temperatures in either direction, with results rounded to at most two decimal places.
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