Celsius and Fahrenheit are two important temperature scales. The Fahrenheit scale is used primarily in the United States, while Celsius is used throughout the world. The two scales have different zero points and the Celsius degree is bigger than the Fahrenheit.

However, there is one point on the Fahrenheit and Celsius scales where the temperatures in degrees are equal. **This is -40 °C and -40 °F.** If you can't remember the number, there is a simple algebraic method to find the answer.

### Key Takeaways: When Does Fahrenheit Equal Celsius?

- Celsius and Fahrenheit are two temperature scales.
- The Fahrenheit and Celsius scales have one point at which they intersect. They are equal at -40 °C and -40 °F.
- The simple method to find when two temperature scales are equal to each other is to set the conversion factors for the two scales equal to each other and solve for temperature.

## Setting Fahrenheit and Celsius Equal

Rather than converting one temperature to another (which is not helpful because it assumes you already know the answer), you can set degrees Celsius and degrees Fahrenheit equal to each other using the conversion formula between the two scales:

°F = (°C * 9/5) + 32

°C = (°F - 32) * 5/9

It does not matter which equation you use; simply use* x* instead of degrees Celsius and Fahrenheit. You can solve this problem by solving for *x*:

°C = 5/9 * (°F - 32)

x = 5/9 * (x - 32)

x = (5/9)x - 17.778

1x - (5/9)x = -17.778

0.444x = -17.778

x = -40 degrees Celsius or Fahrenheit

Working using the other equation, you get the same answer:

°F = (°C * 9/5) + 32

°x - (°x * 9/5) = 32

-4/5 * °x = 32

°x = -32 * 5/4

x = -40°

## More About Temperature

You can set two scales equal to each other to find when any of them intersect. Sometimes it's easier to just look up the equivalent temperature. This handy temperature conversion scale may help you out.

You can also practice converting between temperature scales: