Enter the freezing temperature, average daily air temperature, and total number of days into the calculator to determine the Freezing Index. This calculator can also evaluate any of the variables given the others are known.

Freezing Index Formula

The following formula is used to calculate the Freezing Index. 

FI = ∑ (Tf - Ta) / n

Variables:

  • FI is the Freezing Index (°C-days)
  • Tf is the freezing temperature, typically 0°C
  • Ta is the average daily air temperature (°C)
  • n is the total number of days in the period being considered

To calculate the Freezing Index, subtract the average daily air temperature from the freezing temperature for each day in the period being considered. Sum up these differences and then divide by the total number of days in the period. The result is the Freezing Index in °C-days.

What is a Freezing Index?

A Freezing Index is a meteorological term that refers to the cumulative effect of freezing temperatures over a certain period, typically a winter season. It is calculated by adding up all the degrees of the average daily temperature below freezing (0°C or 32°F). This index is used in various fields such as civil engineering to estimate the depth of frost penetration into the ground or to assess the severity of winter conditions in different regions.

How to Calculate Freezing Index?

The following steps outline how to calculate the Freezing Index:

  1. First, determine the freezing temperature (Tf) in degrees Celsius.
  2. Next, determine the average daily air temperature (Ta) in degrees Celsius.
  3. Next, determine the total number of days (n) in the period being considered.
  4. Next, subtract the freezing temperature (Tf) from the average daily air temperature (Ta) for each day in the period.
  5. Next, sum up all the differences obtained in the previous step.
  6. Finally, divide the sum obtained in the previous step by the total number of days (n) to calculate the Freezing Index (FI).

Example Problem:

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

Freezing temperature (Tf) = 0°C

Average daily air temperature (Ta) = -2°C, -1°C, 0°C, 1°C, 2°C

Total number of days (n) = 5