Calculate discomfort index, air temperature, or relative humidity from any two values using °C and % inputs based on the standard formula.

Discomfort Index Calculator

Enter any 2 values to calculate the missing variable

Discomfort Index Formula

The discomfort index uses air temperature in degrees Celsius and relative humidity as a percent. Enter any two values to calculate the missing value.

DI = T - 0.55*(1 - 0.01*RH)*(T - 14.5)
T = (DI - 14.5*f) / (1 - f)
RH = 100*(1 - ((T - DI) / (0.55*(T - 14.5))))
f = 0.55*(1 - 0.01*RH)
  • DI = discomfort index
  • T = air temperature in degrees Celsius
  • RH = relative humidity as a percentage
  • f = humidity adjustment factor used when solving for air temperature

To calculate the discomfort index, the formula adjusts the air temperature based on humidity. Higher humidity reduces the body’s ability to cool through evaporation, so the discomfort index rises closer to the actual air temperature.

To calculate air temperature, the same formula is rearranged so that temperature is the unknown value. To calculate relative humidity, the formula is rearranged so that humidity is the unknown value.

Discomfort Index Ranges

Use the table below as a general guide. Actual comfort can vary with wind, sun exposure, activity level, clothing, age, and health.

Discomfort Index Typical Interpretation
Below 21 Generally comfortable for most people
21 to 24 Some people may begin to feel discomfort
24 to 27 Many people feel discomfort
27 to 29 Most people feel uncomfortable
29 to 32 Severe discomfort is likely
32 or higher Very high heat stress risk, especially with activity or prolonged exposure

Example Calculations

Example 1: Calculate discomfort index

Suppose the air temperature is 30°C and the relative humidity is 70%.

DI = 30 - 0.55*(1 - 0.01*70)*(30 - 14.5)
DI = 30 - 0.55*0.30*15.5 = 27.44

The discomfort index is 27.44.

Example 2: Calculate air temperature

Suppose the discomfort index is 25 and the relative humidity is 60%.

f = 0.55*(1 - 0.01*60) = 0.22
T = (25 - 14.5*0.22) / (1 - 0.22) = 27.96

The air temperature is about 27.96°C.

FAQs

What does the discomfort index measure?

The discomfort index estimates how uncomfortable warm, humid air feels to people. It combines air temperature and relative humidity into one number. It is not the same as the heat index, but both are used to describe heat stress from temperature and moisture in the air.

Why does humidity increase discomfort?

Your body cools itself partly through sweat evaporation. When relative humidity is high, sweat evaporates more slowly. That makes the air feel more uncomfortable, even if the actual air temperature stays the same.

Can relative humidity results be outside 0% to 100%?

Yes, if the temperature and discomfort index you enter are not physically consistent with this formula, the rearranged calculation can return a relative humidity below 0% or above 100%. In normal weather use, relative humidity should be between 0% and 100%.