How to Convert Celsius to Fahrenheit
To convert Celsius to Fahrenheit, multiply by 9/5 (1.8) and add 32. This guide walks through the method, shows worked examples and explains a quick mental shortcut.
The method in three steps
°F = (°C × 9/5) + 32
- Write down the Celsius temperature. Keep the minus sign if it is below zero.
- Multiply it by 9/5. Multiplying by 9 and dividing by 5 is the same as multiplying by 1.8.
- Add 32. The result is the temperature in degrees Fahrenheit.
Worked examples
Example: 25 °C to Fahrenheit
°F = (25 × 9/5) + 32°F = 45 + 32°F = 77
Example: 0 °C to Fahrenheit
°F = (0 × 9/5) + 32°F = 0 + 32°F = 32
Example: -15 °C to Fahrenheit
°F = (-15 × 9/5) + 32°F = -27 + 32°F = 5
Example: 36.6 °C to Fahrenheit
°F = (36.6 × 9/5) + 32°F = 65.88 + 32°F = 97.88
Example: 200 °C to Fahrenheit
°F = (200 × 9/5) + 32°F = 360 + 32°F = 392
Mental shortcut: double it and add 30
When you only need a rough idea — for a weather forecast, say — double the Celsius value and add 30. It is quick, but it drifts from the exact answer as temperatures move away from about 10 °C:
Common mistakes
- Adding 32 first. Always multiply before adding: (20 + 32) × 1.8 = 93.6 is wrong; (20 × 1.8) + 32 = 68 is right.
- Using 5/9 instead of 9/5. 5/9 is for the reverse direction, Fahrenheit to Celsius.
- Dropping the minus sign. −10 °C is 14 °F, not 50 °F.
- Rounding too early. Keep the full value until the final step, especially for body temperatures like 37.5 °C.
Try it yourself
Frequently asked questions
What is the easiest way to convert Celsius to Fahrenheit?
Multiply by 1.8 and add 32. For a rough estimate in your head, double the Celsius value and add 30.
Why do you add 32 when converting Celsius to Fahrenheit?
Because the scales have different zero points: water freezes at 0 °C but at 32 °F. After scaling the size of the degree with 9/5, adding 32 shifts the zero point.
How do you convert negative Celsius to Fahrenheit?
Use the same formula and keep the minus sign: −15 °C × 1.8 = −27, and −27 + 32 = 5 °F.