Enter all but one of the actual air temperature and relative humidity into the calculator to determine the frost point temperature. This calculator can also evaluate any of the variables given the others are known.

Frost Point Formula

FP = (T - (100 - RH) / 5)

The following formula is used to calculate the frost point temperature. Variables:

  • FP is the frost point temperature T is the actual air temperature in degrees Celsius RH is the relative humidity in percent

To calculate the frost point temperature, subtract the result of 100 minus the relative humidity divided by 5 from the actual air temperature.

What is a Frost Point?

A frost point is the temperature at which water vapor in the air will start to condense and form frost. It is similar to the dew point, but instead of forming liquid dew, the moisture in the air freezes into frost. The frost point is always lower than the dew point and is dependent on the current temperature and humidity levels.

How to Calculate Frost Point?

The following steps outline how to calculate the Frost Point using the given formula:

  1. First, determine the actual air temperature (T) in degrees Celsius.
  2. Next, determine the relative humidity (RH) in percent.
  3. Next, use the formula FP = (T – (100 – RH) / 5) to calculate the Frost Point temperature (FP).
  4. Finally, calculate the Frost Point temperature.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge:

T – Actual air temperature in degrees Celsius = 25

RH – Relative humidity in percent = 80