Temperature conversions between different scales can get pretty confusing at times. If you are used to using the Celsius scale to express your temperatures, you will most probably be thrown off the scale when the units are expressed in a Kelvin/Fahrenheit scale.

Addressing the question of the temperature at which the Celsius scale equals the Fahrenheit scale might sound as a very simple question, and indeed it is. However, it is question that keeps coming up hence the necessity that we address it here even though there are apps that will do automatic conversions.

Well, given that 1°C = 1.8°F

And that, at 0°C, the temperature of water is 32°F

Now, let the freezing point of mercury be X°C = X°F

At temperature T1; 32°F = 0°C

And at temperature T2; X°F = (X-32)/1.8

Therefore; 1.8X = X-32

Solving for X gives (negative)40

The Kelvin scale is equal to the Celsius scale at -40°C = -40°F.