Celsius to Fahrenheit Formula
°F = (°C × 9/5) + 32
The Celsius to Fahrenheit formula is °F = (°C × 9/5) + 32. See why the 9/5 and +32 terms exist, three worked examples, and common mistakes.
The formula is an affine map: a scale factor and an offset.
Why 9/5 and +32?
Fahrenheit splits the ice–steam interval into 180 degrees (32 to 212). Celsius splits the same interval into 100 degrees (0 to 100). The ratio is 180/100 = 9/5.
Fahrenheit’s zero is 32 degrees below the ice point, so after scaling you still add 32.
Steps
- Multiply the Celsius reading by 9/5 (or 1.8).
- Add 32.
- The result is Fahrenheit.
Do not skip the +32. 10 × 1.8 = 18 is a difference, not the absolute reading 50°F.
Three numerical examples
- 0°C: (0 × 9/5) + 32 = 32°F
- 25°C: (25 × 9/5) + 32 = 45 + 32 = 77°F
- 100°C: (100 × 9/5) + 32 = 212°F
Common mistakes
- Using 2×C + 30 as if it were exact. It is only a rough indoor estimate.
- Mixing up 32°C (89.6°F) with 32°F (0°C).
- Applying the formula to a temperature rise. For ΔT use 1°C = 1.8°F with no +32.
Try the numbers
Use the Celsius to Fahrenheit converter or the main Temperature Converter. The reverse derivation is on Fahrenheit to Celsius Formula.
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