Fahrenheit to Celsius Converter
Convert Fahrenheit to Celsius or Celsius to Fahrenheit, with the working shown as a formula.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
°C = °F × 0.5555555556 − 17.7777777778
About this calculator
To go from Fahrenheit to Celsius, subtract 32 and multiply by five ninths. To go the other way, multiply by nine fifths and add 32. The two scales cross at minus 40 degrees.
Worked example
calculated with the default values below
Temperature 72 · Direction ⇄ · Decimal places 4 · From Fahrenheit · To Celsius Result 22.2222 · Kelvin 295.37 K · Input temperature (°F or °C) 72.00
Method and assumptions
C = (F - 32) × 5/9; K = C + 273.15. Absolute temperatures below 0 K are rejected. These are temperatures, not temperature differences.
Data sources
Disclaimer
These calculators give general conversion results. Rounding and the precision of the value you enter both affect the output, so treat displayed decimals as indicative rather than exact.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
°C = (°F − 32) × 5 ÷ 9; °F = °C × 9 ÷ 5 + 32; K = °C + 273.15
- F
- Fahrenheit temperature
- C
- Celsius temperature
- K
- kelvin
Convert the input to the selected opposite scale; the input-scale output repeats the original value. Kelvin is derived from Celsius. Values below absolute zero return an error.
Frequently asked questions
Why is minus forty the same in both scales?
Because it is the single point where the two scales cross. The conversion involves both a multiplier and an offset — five ninths, and thirty-two to shift the zero — and where the offset exactly compensates the scaling, both formulas return the same number. It is a curiosity rather than a landmark on either scale.
How are the Fahrenheit and Celsius scales related today?
The converter uses the exact relationship °F = °C × 9/5 + 32. Zero Fahrenheit is −17.777… °C, not 459.67 degrees below water’s freezing point. The −459.67 °F figure is absolute zero, corresponding to 0 K. Ordinary Celsius–Fahrenheit conversion can be done directly with this formula.
What happens below absolute zero?
Temperatures below 0 K are outside the physical scale, so the calculator shows an input error instead of converting them. The valid lower bounds are −273.15 °C and −459.67 °F.
Which inputs and limits apply to Fahrenheit to Celsius Converter?
Use the units shown beside each field. These are form limits, not recommended settings. Temperature (Fahrenheit): -459.67–10,000; Temperature (Celsius): -273.15–10,000; Temperature (Kelvin): 0–10,000; Temperature (Rankine): 0–10,000 C = (F - 32) × 5/9; K = C + 273.15. Absolute temperatures below 0 K are rejected. These are temperatures, not temperature differences.
What is a complete worked example for Temperature = 72; Direction = ⇄?
Inputs: Temperature = 72; Direction = ⇄; Decimal places = 4; From = Fahrenheit; To = Celsius. Calculation: °C = (°F − 32) × 5 ÷ 9; °F = °C × 9 ÷ 5 + 32; K = °C + 273.15. Results: Result = 22.2222 °C; Kelvin = 295.37 K.