How do I convert Fahrenheit to Celsius without a math degree?
One scale was calibrated around freezing saltwater in 1724, and the other was built around pure water at sea level. Now the entire planet argues about jackets.
The short answer
To convert Fahrenheit to Celsius: subtract 32, then multiply by 5, then divide by 9. Or use the quick mental shortcut: subtract 30 and divide by 2 for a close estimate.
The Exact Formula
(Fahrenheit - 32) × 5 / 9 = Celsius. For example, 68°F becomes (68 - 32) = 36, then 36 × 5 = 180, then 180 / 9 = 20°C.
The Mental Shortcut (within 2 to 3 degrees)
Take the Fahrenheit temperature, subtract 30, and cut the result in half. For 70°F: 70 - 30 = 40, and 40 / 2 = 20°C (exact is 21.1°C). Fast enough to pick an outfit.
The Reverse (Celsius to Fahrenheit)
Multiply Celsius by 9, divide by 5, and add 32. Mental shortcut: double the Celsius number and add 30.
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Common mistakes
- Applying the order of operations backwards by dividing before subtracting 32.
- Assuming 0°F equals 0°C. 0°F is a freezing -17.8°C; 0°C is 32°F.
- Forgetting that -40° is the exact point where both scales meet.