Conversion · General Conversion
Formula verified
Celsius to Fahrenheit Converter
Enter a temperature and pick a direction — the conversion updates as you type, and any value below absolute zero is rejected.
Direction
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Fahrenheit
68
20°C = 68°F
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The exact conversion
Celsius and Fahrenheit don't share a zero point, so converting between them takes both a scale factor and an offset, not just multiplication. Multiply by 9/5 to account for Fahrenheit's smaller degree, then add 32 because 0°C sits at 32°F rather than 0°F. Going the other way reverses both steps: subtract 32 first, then multiply by 5/9.
The formula
°F = °C × 9⁄5 + 32 · °C = (°F − 32) × 5⁄9
Worked example
20°C × 9⁄5 + 32 = 68°F — a comfortable room temperature.
Frequently asked questions
What is the formula to convert Celsius to Fahrenheit?
Multiply the Celsius temperature by 9/5 and add 32: F = C × 9/5 + 32. To go the other way, subtract 32 first and multiply by 5/9: C = (F − 32) × 5/9. Unlike length or weight, this isn't a simple multiplication, because the two scales don't share a zero point — 0°C is 32°F, not 0°F.
Why do Celsius and Fahrenheit agree at −40?
−40°C and −40°F are the same temperature, which looks like a coincidence but follows directly from the formula: setting C = F in F = C × 9/5 + 32 and solving gives exactly −40. It's the one point where the two scales cross, since Fahrenheit degrees are smaller than Celsius degrees and the lines defined by the two formulas intersect there.
Why can't a temperature go below −273.15°C?
That's absolute zero — the coldest temperature physically possible, because temperature measures the energy of moving particles and there's no such thing as negative motion energy. In Fahrenheit, absolute zero is −459.67°F. Entering a value that would convert to something colder than that isn't a valid temperature.
Sources and method
- Celsius–Fahrenheit conversion formula and absolute zero — general published physics.