Source unit
Fahrenheit °F
Fahrenheit is a unit used to measure temperature.
A reading of 1 °F corresponds approximately to -17.2222222222 °C. Differences on an offset scale require interval conversion.
Fahrenheit to Celsius Converter
Reverse conversion: Celsius to FahrenheitConverter
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Fahrenheit to Celsius
Exact1 °F≈-17.2222 °C
How to convert degrees Fahrenheit to degrees Celsius
Formula, method and accuracy
A reading of 1 °F corresponds approximately to -17.2222222222 °C. This is a point conversion, not a factor for intervals.
Subtract 32 from the Fahrenheit value, then multiply the remainder by 5/9. The offset and scale must be applied in that order.
°C = (°F − 32) × 5 / 9
Decimal form: °C ≈ (°F − 32) × 0.55555555555555555556
(1 °F − 32) × 5 / 9 ≈ -17.2222222222 °C
- Operation
- Subtract and multiply
- Method
- Affine
- Accuracy
- Exact ratio
The unit relationship is exact. The visible decimal is rounded according to the current Display setting.
Conversion table
Practical and common reference values
| Fahrenheit (°F) | Celsius (°C) | Copy converted value |
|---|---|---|
| -40 | -40 | |
| 0 | ≈ -17.77777778 | |
| 32 | 0 | |
| 50 | 10 | |
| 68 | 20 | |
| 77 | 25 | |
| 98.6 | 37 | |
| 100 | ≈ 37.77777778 | |
| 212 | 100 |
About Fahrenheit and Celsius
Fahrenheit and Celsius use different zero points and degree sizes. This direction removes the Fahrenheit offset before applying the Celsius scale.
Fahrenheit as the source, Celsius as the result
Use this direction when a Fahrenheit temperature from weather, cooking, healthcare, refrigeration, a thermostat, or imported technical information must be expressed in Celsius.
Result unit
Celsius °C
Celsius is a unit used to measure temperature.
Celsius is the calculation reference for temperature readings in this converter, not necessarily the SI base unit.
Where Fahrenheit-to-Celsius conversion is useful
This direction helps interpret US weather reports, oven settings, thermostats, body-temperature readings, appliance specifications, and technical documents in metric temperature notation.
Subtract the offset before scaling
The exact Fahrenheit-to-Celsius transformation accounts for both scale and zero point. Subtracting 32 first aligns the zero points; multiplying the remainder by 5/9 changes the degree interval.
Operation order changes the answer
Subtract 32 from the Fahrenheit value before multiplying by 5/9. Multiplying first or treating Fahrenheit and Celsius as simple proportional units gives an incorrect absolute temperature.
How this conversion is verified
The reviewed temperature-scale definitions establish the exact offset and scale. The converter follows that same affine calculation for the result and reference table.
Standards used for this conversion
- BIPM: The International System of Units (SI), 9th editionThe Celsius scale and thermodynamic-temperature relationship.
- NIST: Handbook 44, Appendix C: General Tables of UnitsFahrenheit and Celsius conversion relationships.
- NIST: Guide for the Use of the International System of UnitsSI temperature usage and conversion guidance.
For a rough mental estimate, subtract 30 and divide by 2. Use the exact formula for cooking, healthcare, scientific, or equipment settings.
Fahrenheit values below absolute zero are outside the supported physical domain for absolute-temperature conversion.
Frequently asked questions
6 answers for this conversion
- How do I convert Fahrenheit to Celsius?
- Subtract 32 from the Fahrenheit value, then multiply the remainder by 5/9.
- Why must I subtract 32 before multiplying?
- Subtracting 32 aligns the Fahrenheit and Celsius zero points. The 5/9 factor then adjusts the degree size.
- Does a Fahrenheit temperature difference use the same formula?
- A temperature difference uses only the 5/9 interval factor. The 32-degree offset applies to absolute temperature readings.
- Why can a Celsius result contain a repeating decimal?
- The exact 5/9 scale can produce a repeating decimal for some Fahrenheit inputs. The displayed result is rounded while the relationship remains exact.
- What happens below absolute zero?
- Values below absolute zero do not represent valid absolute temperatures, so the converter rejects them rather than returning a physically invalid result.
- When is Fahrenheit-to-Celsius conversion useful?
- Use it for Fahrenheit weather, oven, thermostat, body-temperature, refrigeration, appliance, or technical values that require Celsius.
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