Celsius to Fahrenheit Calculator: Temperature or Difference
Convert Celsius and Fahrenheit in either direction. Distinguish absolute temperatures from temperature changes and reject values below absolute zero.
Your inputs
Choose absolute temperature or temperature difference before calculating.
Your result
Enter your values, then choose Calculate.
Calculated from your inputs and the assumptions below. Displayed results are rounded; inputs are not sent to a calculation server.
Calculation breakdown
Method, assumptions and worked example
For an absolute temperature: °F = °C × 9/5 + 32, and °C = (°F − 32) × 5/9. For a temperature difference, use only the scale factor: Δ°F = Δ°C × 9/5. Do not add or subtract 32 for a difference.
Worked examples
An absolute temperature of 20°C is 68°F. A rise of 20°C is a rise of 36°F. Water’s familiar reference values are 0°C = 32°F and 100°C = 212°F, while −40 has the same numerical value on both scales.
Absolute-zero boundary
The absolute mode rejects values below −273.15°C or −459.67°F. The difference mode accepts signed changes without applying that absolute-temperature boundary. A difference alone does not establish a physically possible starting or ending temperature.
Choose the quantity type before interpreting the output. A thermometer reading and an increase between two readings are different calculations. Swap direction preserves the current converted value, and rounding is applied only when displaying the answer.
Frequently asked questions
Why does a 20°C change equal 36°F rather than 68°F?
Differences use only the 9/5 scale factor. The 32-degree offset applies to absolute readings.
Can I enter negative temperatures?
Yes. Absolute values must remain at or above absolute zero; signed temperature differences use a separate mode.
Method review and references
Formula and content reviewed on 10 October 2026. Worked examples are hypothetical. Conversion definitions and calculation assumptions are stated below. Carrier and campaign terms must be supplied by you.